Doesn’t Steam run basically everything, including the client itself, inside the Steam Container Runtime now? No Steam games, native or not, use the system libraries anymore. I know I occasionally need to wait a couple of seconds after an update for it to update the Steam Container Runtime before even starting the client, which makes me think that they run the client in the container as well. I think the only real 32-bit dependency it has on the system is the user space graphics driver.

“Free” memory is actually usually used for cache. So instead of waiting to get data from the disk, the system can just read it directly from RAM after the first access. The more RAM you have, the more free space you’ll have to use for cache. My machine often has over 20GB of RAM used as cache. You can see this with free -m. IIRC both Gnome and KDE’s system managers also show that now.