jj-spr solves this, although it is still pretty buggy: https://github.com/LucioFranco/jj-spr
This is something GitHub should be investing time in, it’s so frustrating.
I've been going through a lot of different git stacking tools recently and am currently quite liking git-branchless[1] with GitHub and mergify[2] for the merge queue, but it all definitely feels quite rough around the edges without first-party support. Especially when it comes to collaboration.
Jujutsu has also always just seemed a bit daunting to me, but this might be the push I needed to finally give both jj and tangled a proper try and likely move stuff over.