How do Unitarians explain Hebrews 1:10-12?

This is a reference to God who created all things aka Gen 1.

It is being re-applied to Jesus. Not to rewrite what was truth, but to add another dimension to it.

We see this pattern with an Immanuel in Is 7:14 and Matt 1:33. The two have no factual connection but the similarities are reapplied with a new focus on the Christ. Many OT passages had fulfilment in their day, but as God designed in to His plan, have much greater significance in Christ.

We can read on to Heb 2:5

5 For He did not subject to angels the world to come, about which we are speaking.

So the context is now evident. Quoting an OT passage and focussing on a new application of it on Christ. This does not undo what was true, but adds the depth God designed in to His word of promise.

Jesus as the firstborn of a new age (Col 1:15,18), which includes all men as brethren (Rom 8:29), is the one who may take the credit for what he accomplished on the cross when he declared, ‘it is finished!’

We can see the initial thread of the message from v1

1 God, after He spoke long ago to the fathers in the prophets in many portions and in many ways, 2 in these last days has spoken to us in His Son, whom He appointed heir of all things, through whom He also made the ages. This last word (ages) is usually translated world or universe which is grossly incorrect. Heb 1:1-2

So Jesus is the figurehead of a new age, even the creator of it as the man given all authority by his Father - and duly deserved!

So the Heb reference in focus is a reiteration of an old glorification of God, now being shared with His triumphant son by the writer of Hebrews.

Jesus being made heir is an absurd concept if (as many presume) he made everything to begin with.

https://www.biblicalunitarian.com/verses/hebrews-1-10 For more info.

To properly interpret Hebrews 1:10-12 it is important to put everything in context. First, the series of arguments the author gives are to show 1 thing: that Jesus has BECOME greater than the angels because he has inherited a greater name.

We must also see the structure of his arguments. He gives 3 with 2 points for each argument. He gives one point then gives the second with δε or "but". When he starts a new argument, he uses καί or "and". In addition, when quoting scripture, not God, he uses λέγει or "it says" but when quoting God, he uses είπεν or "he said". If not specified, it is the last word he used. This adds up when looking at what is being quoted. When the quote is something God actually said in the original context, he uses "he said", but when the quotation is anyone else he uses "it says" meaning scripture.

So in verse 5: God said... And also God said... verse 6: but (second point of first argument) it says... verse 7: and (new argument) to the angels it says... verse 8: but (second point of second argument) of the son it says... verse 10: and (new argument) it says (implied by previous wording)... verse 13: but (second point of third argument) to which of the angels has God said...

The first is that Jesus is the begotten Son of God who was begotten as some point in time, meaning he became the son and therefore became greater. This is apparent because the angels are told to worship God's firstborn. The second argument is he can make even the wind an angel, but about the son, God is his throne forever.

Then the third argument which is what you asked about. Sorry for the long explanation, but I had to go through all that to establish context. Again, the context is how Jesus BECAME greater than the angels. Verse 10 is not about the son. It does not say that. It is the start of a new argument. The author simply states that YHWH is creator, but that creation will pass away, but YHWH remains. And verse 13, he uses δε, indicating a second point of the same argument. And his argument is that Jesus was appointed to the right hand of God, but no angel has been appointed like that. Jesus was appointed Lord over Creation as the author goes on to say in chapter 2. He is the last Adam, or how Adam should have been. Adam was appointed as Lord over God's creation, but then rejected God's rule and accepted the rule of the serpent. Jesus was completely obedient unto death, and therefore was appointed back to where humanity should be.

Again, verse 10 is not attributed to Jesus, it is merely a statement which was originally about YHWH and is still being stated as true about YHWH. The author then uses that truth to state that Jesus BECAME greater than the angels by virtue of being appointed to God's right hand and subsequently over all of that Creation.

This is a different interpretation than some Unitarians, I find it much more plausible. Hope this helps. Here is a video of the same interpretation. He goes into more detail and argues quite well: https://youtu.be/4aDlN2pKv3Y