+1 to this idea
Oh heck yeah. Plex would be a great fit for the Steam Deck - bonus points if you can navigate with the controller natively.
This would be pretty good, if the Plex had its app on Steam, so I could launch it on my future Steam Deck, and if I could sync my tv series into it. That would be perfection!
Edit: Plex HTPC installed via Discover app on Steam Deck works really well, especially if you use controller configuration from Ledow.