As nitefox said already, you can start the steam deck on desktop mode and it’s already running Linux with KDE. My first thought when I read your post was also that Steam Deck could be exactly what you need. Plus they just refreshed it with better thermals, battery life, and display. A usb c dock would get you a pretty decent dev machine on a budget. Plus it’s great for retro gaming.
Plexamp can do all of this (not sure about mdna speakers though) and it has Tidal integration.
Finamp will also work but it lacks library/genre radio and mix support last time I checked.