it’s not a setup issue, it’s a hard limit of xorg. maybe having two xservers may help, but then you wouldn’t be able to move windows between them. the way multiple monitors are done using x is that they’re treated as one continuous screen, but that means it can get a bit wacky because they’re not the same.
Snaps are a closed-source proprietary packaging format that Canonical controls. And they have also altered apt on Ubuntu to download snaps first before native packages. You may be using snaps right now without realizing it, which is also part of the issue.