Are you sure? I'm pretty sure I had two tabs, one for picking displays and other for picking windows. Pretty much like this: https://bug1675764.bmoattachments.org/attachment.cgi?id=9186...
"Will this let me share individual windows?
No, only entire outputs. It would take significant work in wlroots, and likely a new protocol, to make this possible. A second rendering pass would be required, which would significantly reduce wlroots performance, so this may not be implemented any time soon (or ever).
Will this let me share all of my outputs/displays at once?
Not yet, no. It will likely never create a single stream that combines all of your outputs, but once we implement better output selection, there is no reason xdpw cannot create multiple simultaneous streams of different outputs."
So it looks like I'm shit out of luck for quite a while on sway/wlroots. Looks like Gnome figured it out. Not sure about KDE.
https://github.com/emersion/xdg-desktop-portal-wlr/issues/12
I.e. it's not that the tech stack or architecure is the wrong it's simply not done yet and not done to the point it's a bit silly to blame Slack for not enabling it.
It's also not the fault of wayland/pipewire/chromium/electron/slack for not all simultaneously releasing working screen sharing but it is a mistake to say you can switch from X11 to <Wayland stack> and not worry about screen sharing.
I use pipewire for screen sharing, I like it, but its not a fully baked stack and won't be for some time yet.