There’s a lot I could say about this. The speaker in Isaiah 44 is God the Father, because in Isaiah 42:1 He refers to the Messiah as “my servant,” and the speaker remains consistent throughout the next several chapters. However, I think it is possible that “Thus saith the Lord the King of Israel, and his redeemer the Lord of hosts” (Isaiah 44:6) denotes two distinct persons. “The Lord the King of Israel” is the Father, and “his redeemer the Lord of hosts” is the Son, who commands the heavenly hosts in the New Testament and redeems the world. In that case, “I am the First and the Last” would be a joint-statement made by both the Father and the Son. This makes a good deal of sense in light of the fact that both the Father and the Son share the title “the First and the Last” in the book of Revelation.
So in Isaiah 42-48, the person making all the monotheistic claims is the Father. The Father is the First and the Last, and beside Him there is no God. But since the title “the First and the Last” is applied to the Son in Revelation, we know that He must be everything that title signifies together with the Father: the Father and Son are the First and the Last, and beside the Father and Son there is no God.
I suspect part of what motivates your question is that if Person X says “I alone am God” that excludes any person other than X from saying “I am God.” But I don’t think this is the case. Perhaps this illustration can help. If I hold up a gospel (i.e., a booklet containing the four gospels) and say “I deny every gospel except this one,” I am not really talking about the particular booklet I’m holding (the “hypostasis”), but rather about the contents of that booklet (the “nature”). So if I pick up a different gospel (i.e., a different booklet) and say “I deny every gospel but this one,” I am uttering a true statement because the content of the two booklets is identical, even though the object of my affirmation is a numerically different booklet than the first one. I predicate the word “gospel” of both the booklet and the contents of that booklet, which allows me to say “I deny every gospel except this one” for each booklet I pick up. The booklets are many, but the content is one. In a similar way, we predicate the word “God” of each hypostasis of the Trinity, and we say “Besides this hypostasis there is no God.” But we also say this for the other two hypostases, because the nature of the three hypostases is one.
I initially wrote that in response to a unitarian who asked a similar question. I know your concern is slightly different since you’re (rightly) trying to include the Son and Spirit as the Creator of the world. But the same logic applies here as well, I think.
You may not be aware of this, but I think that very often in the Old Testament, YHWH is the Son of God. So there are other passages in which  YHWH makes monotheistic claims and  it’s a single person speaking, and the single person speaking is the Son. An example of this is [Nehemiah 9:6]
“Thus says the Lord, the King of Israel,
And his Redeemer, the Lord of hosts:
‘I am the First and I am the Last;
Besides Me there is no God.
7 And who can proclaim as I do?
Then let him declare it and set it in order for Me,
Since I appointed the ancient people.
And the things that are coming and shall come,
Let them show these to them.
8 Do not fear, nor be afraid;
Have I not told you from that time, and declared it?
You are My witnesses.
Is there a God besides Me?
Indeed there is no other Rock;
I know not one.’ ”
Remember these things, O Jacob,
and Israel, for you are my servant;
I formed you; you are my servant;
O Israel, you will not be forgotten by me.
22 I have blotted out your transgressions like a cloud
and your sins like mist;
return to me, for I have redeemed you.
23 Sing, O heavens, for the Lord has done it;
shout, O depths of the earth;
break forth into singing, O mountains,
O forest, and every tree in it!
For the Lord has redeemed Jacob,
and will be glorified in Israel.
24 Thus says the Lord, your Redeemer,
who formed you from the womb:
“I am the Lord, who made all things,
who alone stretched out the heavens,
who spread out the earth by myself,
I asked for Theophilus’ thoughts on an argument dealing with Isaiah regarding the issue of whether in scripture the Trinitarian persons talk as if they are one person. I think his interpretation could be used to undermine trinitarianism in the Old Testament and make the other persons devoid of any creative activities, contrary to passages that teach otherwise.
In these passages, Yahweh/God/etc refer to merely the Father(in contradistinction to anything or anyone else). So, it seems as if the Father claims to be divine alone. He also claims to have created the world and forming it alone. We have ample reason to think this is obviously not the case:
He may try to reinterpret these verses in the light of Nicene distinctions. So, he may say this passage is about God being the sole originator and therefore not excluding the divinity or creatorship of the other persons of the Godhead in other senses. The problem with this moves it that the passage doesn’t state this fairly technical point of Nicene Orthodoxy. That is similar to dispensationalist methods of interpretation. The text is written in the light of contrasting the Biblical God from the ANE gods and not to distinguish the persons of the Godhead with thoughts that hadn’t developed yet. Secondly, it would entail that God may have had other gods to assist him with his act of creation. They wouldn’t be the sole originator but merely secondary one’s(like the other persons of the Godhead or Gnostic/2nd temple intermediaries). Thus, it undermines Isaiah’s purpose of a robust monotheism.
Secondly, he recognizes the NT writers quote this passage with reference to Christ in the New Testament as him being the “First and I am the Last”. This hardly is a singularity. Jesus is identified with Yahweh/God/ etc multiple times by various NT authors. John mentions about how Isaiah saw his glory(John 12:41, Isa 6), John mentions about how Jesus identifies himself as the God appearing to Abraham while making reference to the Divine name ego eimi (ani hu)(Isa 41:4, 43:10, 46:4), and even in the next chapter with everyone bowing their knees confessing him as LORD(Isa 45:23, Rom 14:11, Phil 2:10-11).
Thirdly, he gives an example of which he uses to frame the way the Father can say “I am alone God” and yet the other persons are God as well. The problem is the meaning between these two things are different. The gospel(or any such booklet) is merely a generic form of that message, but the Father has no generic forms of himself. There is merely 1 Father. If that was the only version of that book, then it would be merely that one booklet. The prior statement was never meant to imply this very book is the only book that exists in that class and that you believe. The divine statements are about his unique existence. The message of the gospel can be instantiated in many different forms and venues, but God is not the same. These verses posit that there is merely 1 creator of the heavens of the Earth and God of the world. It is a calling card to monotheism. While the message in a book can be replicated, the creator of the world does not share in that characteristic. So, it seems this logically limits whatever is being claimed in these passages uniquely to the subject of which it is speaking. If the Father, then the Father alone.
Fourthly, this robust hermeneutical principle puts us in a place of skepticism with what can be predicated of the persons. The Bible predicates things of God/Yahweh that may merely refer to the Father:
8 Anyone who does not love does not know God, because God is love. 9 In this the love of God was made manifest among us, that God sent his only Son into the world, so that we might live through him.
God here refers to the Father, but yet we often think this is true of God qua his nature and therefore the Son is love because he possesses the nature given to him by the Father. The issue is exegetical this is arbitrary(given Theophilus’ rule) to assume this is true across the person’s of the Godhead. Why isn’t love merely of the Father because of his monarchy? It’s tied with him sending the Son into the world.
Fifthly, it seems to me that a better alternative already exists for explaining these things and yet are affirmed by proponents of Nicene Orthodoxy. Cameron Brinkman:
Here, one person of the Godhead is speaking to one specific prophet. Since each person is the Divine Essence, each one can honestly say that “I YHWH (a personal essence that is identical to the person) do these things”. The persons just are the Divine Being. No other being is necessary, which the name YHWH expresses.
Hezekiah can declare that YHWH alone made heaven and earth. No numerically distinct concrete object assisted YHWH in the job.
The Father or the Son can say, “It is I, who alone make all things”. All Divine persons share in the act of willing. It is a rule that all three persons are equally involved in the ad extra works of the Godhead.
Indeed, both the Father and the Son can say together that “I alone created the heaven and the earth,” because each just is the Divine Essence, which created the universe. Neither can say that “I am the only person who created the earth”, because all three persons created the earth. But the exclusive descriptor is not intended to exclude other personal agencies, but other substantial agencies like idols, which are expressly creations. But since Jesus is believed to the eternal and divine by all Orthodox Trinitarians, this is no problem. Perhaps one could object to Trinitarianism on other grounds, but to do so based on a passage like Isaiah 44 alone would be to beg the question.
Indeed, no being or concrete entity that is not able to utter “I, YHWH, created the universe” is capable of sharing agency with YHWH in the creation event. But Jesus can pronounce the statement justly — He is YHWH. Therefore, Jesus is not removed from the Godhead by the proposition.