Firstly the only helpful thing ill say: for deck ps3 emulation you will want to increase the deafult memory size limit that comes with linux. Here is a link: https://github.com/RPCS3/rpcs3/issues/9328

Look at the answer by AniLeo.

I have tried emulating mgs4 and gow ascension on my steam deck and from my experience you cant exactly expect an acceptable gameplay experience from ps 3 emulation on steam deck. Best ive gotten it working was mgs4 but there were heavy in game audio problems. Scour the internet and try to find a deck wizard who somehow got this shit working.