yes, it doesn’t run plasma when it’s in big picture, it runs it in https://github.com/ValveSoftware/gamescope along with other tweaks, so it’s lower overhead and game windows tend to behave better

it also handles updates to os as well as to steam so you don’t ever end up with an update that breaks steam, they’re always in sync

I don’t know if steam big picture use gamescope https://github.com/ValveSoftware/gamescope.

I would guess it doesn’t, but I cannot be 100% sure, I haven’t used steam on my laptop since ages