In that case you could maybe see if it works correctly for you in firefox installed via flatpak from flathub. Those are official builds and bug reports on them should go to Mozilla directly.
It could be related to hyprland though. I think I read somewhere that one of those lightweight WMs (or whatever it really is idk sry lol) doesn’t ship a portals config file for x-d-p to exactly know which exact implementation to use. Maybe arch doesn’t have that issue though