Good thought. I see some potential issues though.

I’m not well versed in how steam handles things like saves, configs, etc. I would think if those are saved in the steam apps folder, then they are indeed written on the location the game is saves. RO would also prevent updates as well.

Overall I think the writing to disk is much less of a concern than say having a whole OS on there.

Does RPi’s Raspbian support any boot moad like “toram?”. I have no idea what size those OSes are for a pi, but I wonder if things like that would help too. I know some OSes are designed to be less write-intensive to prevent some of this as well.