On debian testing (trixie):
$ cat bin/steam-jailed.sh
#!/bin/sh
firejail --private=/home/user/steamjail --profile=/etc/firejail/steam.profile ~/steam $1
Sometimes an update breaks something, and I have to experiment with the profile settings, for which it helps to launch a bash with the same jail and start steam on the command line inside the jail to see output messages.
#!/bin/sh
firejail --private=/home/user/steamjail --blacklist=${HOME}/.inputrc --profile=/etc/firejail/steam.profile bash
What happens most of the time is that a steam update depends on a newer system library that I didn’t yet install and I then have to do a system update - steam is shit at managing OS dependencies (i.e.: it doesn’t)
Did you get it running already? If so, happy to have helped :) It’s a bit tricky to move your downloaded games into the jail so that you don’t have to re-download, I think maybe it’s just easier to download them again as you start playing them. I started with a jail right from scratch so I only ever tried moving my games files between different jails, that was easier (but can still be done wrong).