Ullebe1

Even people on Arch should use it. It ensures better isolation of processes and is the only supported installation method if you ever have issues.

That seems like a shortcoming in those tools, that I’d expect them to fix as Flatpaks are pretty commonplace.

It uses FCM for the notifications.

Proton uses XWayland, this is for proper, native Wayland support. It will make its way to Proton eventually.

Yup, and I believe it even does it automatically if it fails to reach the desktop for a number of boots in a row.

Depends on which DE in which version it is using, but anything with recent Gnome (Fedora, Ubuntu) will. Not sure if KDE distros generally default to it, and for more niche DEs the answer is probably “no”, unless it was explicitly made for Wayland.

I doubt it’s ever going to be a part of the core protocols, but it doesn’t have to be, you can just use Waypipe.