Let's open this one up once more:
https://feedback.substance3d.adobe.com/forums/257908-substance-3d-designer/suggestions/8660929-8k-and-possibly-16k-texture-resolution-support

Because it's simply only half way completed!

I'd suggest it's time for 16K and higher!! I mean it was time for that two years ago... so where are we at here? I do not understand why I cannot work on 16K yet. It's 2022 and MANY people could need this!

Also, yes you've introduced 8K but in designer in the "new project/graph" window, it cannot be selected. No, one has to create the 4k graph first and then set the parent size in there... Also a little annoying behavior