PSA: if you don't want your Steam overlay being visible at all in #OBS on #Linux, turns out it's pretty easy to tell Vulkan to have it capture just the game (and optionally MangoHud) but not the overlay. Here's #EliteDangerous demonstrating that.
This is on Nobara 40 running #KDE Plasma 6 on Wayland, but will probably work on other distros.
https://github.com/nowrep/obs-vkcapture/issues/14#issuecomment-2514601539