Dude, wheres my Microsoft Visual C++ Redistributable?
The answer: it didnt, at first.
Most of the time.

Come on, Proton lad, youre kinda dropping the ball here.
This worked a treat for me, and I didnt suffer any further compatibility headaches from there on out.
Not just for the sake of smoothness, but to appease the games paralysing mistrust of suboptimal performance.

Thats not ideal, clearly.
But its also a rarity much more often, The First Descendant feels fine on the Deck.
Youre still getting 30-40fps in the most demanding areas, maybe mid-forties in tight interiors.
And again, frame generation isnt as useful as it sounds.