To be clearer, as each wayland desktop pretty much creates their own incompatible wayland compositor (because wayland protocol is minimal and not feature complete) this is just a guide to fixing the hyperland broken wayland desktop. Not all waylands' broken desktops.
What protocol is missing from Wayland?
Yes Wayland doesn't have a printer protocol like Xorg, I know.
https://gitlab.freedesktop.org/wayland/wayland-protocols/-/t...
This is an incomplete list of protocols that aren't part of core Wayland. Compositors implement additional protocols that aren't even part of this process (e.g. wlr-screencopy-unstable). See the wlroota protocols here: https://gitlab.freedesktop.org/wlroots/wlroots/-/tree/master...
Right but there's the xdg-portal for screen capture which runs through Pipewire and supports sand-boxing (because its negotiated over dbus), which all the main compositors support.
Just because a protocol isn't part of Wayland, doesn't mean a standard protocol does not exists.
The big ones missing for me are accessibility support (ie, screen readers) and mouse/keyboard input support for basic things like keyboard sharing.