Agree with Frozen here. Outside of AppImages which can go where ever (I usually do /opt) I would let most things install where they default to. I installed steam directly from their repo (not s76/ubuntu/debug repo) And had no issues. I have an additional drive in that has a specific mount point in my home dir and games install there. Sounds like you may be new to Linux? It takes a bit to get used to the different mindset of Linux but I’ve found over the years that backing up my apps isn’t really as big of a deal in Linux, especially these days with flatpak and snaps and appimages, etc. I’d be more worried about storing media (photos, videos, music, etc) in its own drive or partition. if you are new to Linux and I’m not projecting here, you should think about joining the PopOS Mattermost. A lot of good folks there always willing to help.
Welcome to the cult….
Ha, indeed.