The Deck can output up to 4K 60Hz with the right dock, so the picture quality is not going to be limited by the supported resolution of the Deck. What will limit the picture quality is that SteamOS by default runs games at 1280x800 or 1280x720 for 16:9 external screens, regardless of the actual selected resolution. It will upscale games rendered at 720p to whatever the actual output resolution (1080p or 4K) is. There is an option in the per-game settings in the SteamOS UI to set the resolution for each game. If you pick Native, it will allow the game to render up to the screen’s native resolution for a full-quality image, no different than you would get on a normal PC. However, the Steam Deck’s GPU isn’t very powerful compared to a desktop PC so you aren’t going to be able to push most games that high. A lot of older titles and 2D games can run fine at native 1080p on the Deck though.
Hopefully Qualcomm takes the hint and takes this opportunity to develop a high performance RISC V core. Don’t just give the extortionists more money, break free and use an open standard. Instruction sets shouldn’t even require licensing to begin with if APIs aren’t copyrightable. Why is it OK to make your own implentation of any software API (see Oracle vs. Google on the Java API, Wine implementing the Windows API, etc) but not OK to do the same thing with an instruction set (which is just a hardware API). Why is writing an ARM or x86 emulator fine but not making your own chip? Why are FPGA emulator systems legal if instruction sets are protected? It makes no sense.
The other acceptable outcome here is a Qualcomm vs. ARM lawsuit that sets a precedence that instruction sets are not protected. If they want to copyright their own cores and sell the core design fine, but Qualcomm is making their own in house designs here.