I remember this lol, to be fair no one knew how the guy managed todo it, because steam(the launcher) has checks for that, they assume the guy tried to run the steam command instead of clicking the launcher(don't do that)
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.
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).