Looking deeper into it (been meaning to anyways) it seems to be the typical Wayland compositor specific issue, and ironically I'm using ddevault's compositor sway. Pipewire doesn't seem to care what you send it but your second window looks to be part of xdg-desktop-portal-gtk if I'm not mistaken. Since I'm using sway/wlroots I need to use xdg-desktop-portal-wlr instead. In the FAQ for this package:

"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.