𝒍𝒆𝒎𝒂𝒏𝒏

In desktop mode there is an easier way for the last part - click the battery icon in the taskbar, then click “temporarily don’t sleep”. Screen brightness can also be set in the same area

No quick solution for turning the screen off though AFAIK…

Edit: rephrasing post

I would suggest Plex HTPC on the deck instead, since it works really well with the deck’s gamepad in the normal gaming mode. Touch also works but should probably be considered a last resort IMO