Let's look at the context. I am open to differing ideas. If it is saying something other than the new earth, so be it.
And I know you are open as well. While some here have said they can't change their mind, we have both done so at times in these forums and otherwise.
Isa 66:15 “For behold, the LORD will come in fire, and his chariots like the whirlwind, to render his anger in fury, and his rebuke with flames of fire.
Isa 66:16 For by fire will the LORD enter into judgment, and by his sword, with all flesh; and those slain by the LORD shall be many.
This discusses a time of judgment against all flesh.
Isa 66:17 “Those who sanctify and purify themselves to go into the gardens, following one in the midst, eating pig's flesh and the abomination and mice, shall come to an end together, declares the LORD.
Isa 66:18 “For I know their works and their thoughts, and the time is coming to gather all nations and tongues. And they shall come and shall see my glory,
This judgment involves gathering all nations
Isa 66:19 and I will set a sign among them. And from them I will send survivors to the nations, to Tarshish, Pul, and Lud, who draw the bow, to Tubal and Javan, to the coastlands far away, that have not heard my fame or seen my glory. And they shall declare my glory among the nations.
Isa 66:20 And they shall bring all your brothers from all the nations as an offering to the LORD, on horses and in chariots and in litters and on mules and on dromedaries, to my holy mountain Jerusalem, says the LORD, just as the Israelites bring their grain offering in a clean vessel to the house of the LORD.
Jerusalem is mentioned, which places it either at the location of current Jerusalem, or the new Jerusalem from above. Note the themes of carrying back Israelite brothers from captivity.
There is also reference to grain offerings, etc. This is why I think the initial point of these promises was a time of covenant blessings after the restoration from captivity.
Isa 66:21 And some of them also I will take for priests and for Levites, says the LORD.
In the new covenant all are priests, and the levitical tribe is not the focus. Again this seems to point to old covenant language, in a restoration after judgment on the nations.
Isa 66:22 “For as the new heavens and the new earth that I make shall remain before me, says the LORD, so shall your offspring and your name remain.
Isa 66:23 From new moon to new moon, and from Sabbath to Sabbath, all flesh shall come to worship before me, declares the LORD.
Now it states as the new heavens and new earth remain, so shall your offspring remain. This seems to at least put it in the time period of a new heaven and new earth. The question is whether this is talking about the same new heaven and new earth as John and Peter.
Given the earlier reference to assembly at His holy mountain, it sounds like this would be on earth.
Isa 66:24 “And they shall go out and look on the dead bodies of the men who have rebelled against me. For their worm shall not die, their fire shall not be quenched, and they shall be an abhorrence to all flesh.”
Whether you take this of an earlier judgment when God judged the nations, or at the final judgment, both seem to point to the bodies being on the earth, rather than in heaven, etc.
There are other texts where Isaiah speaks of the new earth, etc. and those have similar elements which seem to point to a possible time of covenant blessing. But I think these are ultimately fulfilled in a different way through the new covenant due to disobedience.