You can pretty much use the game deck rating based on your experience with a PC, platinum rated games no experience and down from there.

As an experienced PC gamer I’ve never bothered with TDP and you pretty much ignore that for every game.

in terms of Proton unfortunately its something you will have to interact with… my advice, if you are considering buying a game, check protondb first it will let you know if there is anything to worry about

I bought Darksiders: Warmaster Edition for my steam deck, my hands are literally aching from the paces this game has put me through, both brutally hard and thoroughly rewarding and mind boggling frustrating to sometime ingenuous in its design. I don’t think I’ve ever had a game that I simultaneously love and hate at the same time :-)