i really like niri but one thing i've noted that i can't tell if it's a niri thing or xwayland-satellite thing but games almost never fullscreen properly
some games like tf2 will fullscreen at launch but will go into windowed mode as soon as the window unfocuses (this also crashes steam for some reason)
I can Mod+Shift+F to fix it but it's not the best workaround and it breaks Steam Game Recording