I’ve been doing PC gaming for my whole life (I am also almost 29 yo, so under 30) on Windows desktops or laptops (gaming ones). Never had a console in my life except the ps2 when i was a kid (my brother’s ps2). But I can assure you I had to learn quite much of stuff anyway since Linux PCs are quite different. This said if you’re new to PC gaming you can just buy everything on Steam and you’re good to go. Instead I have bunch of stuff on other launchers (because on Windows I don’t mind) and I had to go through some youtube guides to get them working nicely on the Deck. But once it’s done once it’s done forever! so I can now keep staying in gaming mode except if I want to install some more games from battle.net or Ubisoft (with Epic, GOG and Amazon I can use Heroic directly from gaming mode). But I installed some and I will be good for a while

With diablo 4 yeah I tried also FSR 2 in quality. But nothing for me the characters just looked like they were out of focus and I couldn’t enjoy it. I’ll play D4 only from my laptop

You just mentioned the only two games I think they look horrible on Deck (I have an oled 512) 😅😅 I even tried to stream them from my PC to see if with ultra settings it gets any better but they just look very awful. They are just not made to be played at 800p. I would suggest to play them on at least a 1080p screen

Tried it on my oled 512 and D4 just looks very bad even at ultra settings and hdr on, the environment is nice but characters and the enemies just seemed out of focus and washed out. I think this game just looks bad at this screen resolution because on my laptop the game looks great

I added YouTube and Disney plus through emudeck and they look great! Still have to try paramount plus. Prime video instead looks like shit, from what I understand they don’t support over 480p on Linux devices

I don’t have a 4090 but a quite powerful RTX 3070 laptop.

I tried streaming with moonlight on my oled deck: Hogwarts legacy, Diablo 4 and R&C Rift Apart. HL and D4 just look bad on the Deck even with streaming. I think these two games just look bad at 800p no matter what gpu you have behind (they both look great on a 1080p screen). And BTW Diablo 4 looks bad also if run on the Deck directly. Rift apart instead looked quite good. I think recent triple AAA games for the majority just look bad at 800p. I decided I’ll use my deck just to play indies and lighter or older games (The Witcher 3 looks good for instance). At that it is GREAT, but with recent AAA games it think it’s just better to play them with dedicated Gpus and at least 1080p screens.

In summary, I think it’s pretty useless to use a powerful GPU in streaming with the Deck. Just play lighter games on the deck directly