Is it under AGPL-3.0 as telled in CurseForge? https://www.curseforge.com/project/681792/license
dont make us worried if u turn it ARR

Probably it will turn to ARR as Create: Astral 2.0 removed all licensed textures from Cabriclaity under AGPL/GPL 3.0 so it's free to change its license now.

I know it could, and i wonder if it would

I am not informed well on licensing, and I prefer keeping it relatively open for contribution from the community. What would be the right place to find which license to choose in this case?

You mean where to put the LICENSE file?
I think the root of repo is an option
That GitHub can analyze the LICENSE file matters

It cannot mean how to choose which LICENSE to use right ... ?

f88e5ac