The Last of Us was originally done by Naughty Dog. The last game from Naughty Dog, that was ported was Uncharted, and Iron Galaxy did the port. 
Seems logical on some level.
It looks like Nixxes focuses on ports from Crystal Dynamics, IO Interactive, Eidos and Insomniac Games.
If you follow the history of work, and check the original dev’s, it tracks just fine. Any current unoptimised games, seems more to be a sign of the publisher putting pressure on devs to finish the work with an immovable deadline, rather than telling them, if you need the time to make quality, then take it.
Oh and while I’m here, looks like barely 30fps experience on the Steam Deck. Perhaps it’s too heavy for that hardware.