You're missing the point. When you run an x client in wayland, you are still running an x server. Every vulnerability an x server has, xwayland has. I don't need to name anything specific because you can legitimately go and look this up yourself.

Don't think you are fully safe from keylogging in xwayland either, you are only safe from keylogging in wayland apps, xwayland clients can keylog other xwayland clients because x servers can see other x servers, in other words, they are all still very much running seperate PIDs on your system which means at the very least they can still touch each other. XWayland, by default, does not really sandbox clients because why exactly would it need to? Do you realize exactly how much of a feat that would take to truly isolate an x server from the rest of your system? That is an inherent flaw with X itself because X never set out to acheive those goals in the first place.

If you are at the point where you have to be worried about protecting your xsession or wayland session, you need to make a fresh install and tighten your security accordingly. All that tightening down your window manager does is make an attacker go for a lower hanging fruit on your system, that's why you should make your machine unfeasible to even attack in the first place. You can go run around and try to tighten every little nook and cranny, but if someone is determined to get into your system, they will eventually get in. The malicious parties we are trying to defend against with general security practices are not nation state hackers, they are skids and standard malware.

Yes, one is scaled 2x, I have a 4k60 and a FHD165. I'd recommend doing this with your autostart script using xrandr