Is this "Wayland changed the way screen sharing works, which broke slack and everything else that does screen share" or "I've gotten screensharing working with everything else but it's still broken in slack"?
I don't use slack so I'm not sure what the specific issue is, but I remember having to install additional packages on Arch (BTW) to get screen sharing working in Plasma (my three use cases being discord, Google meet, and steam remote play).