Question regarding sharing Steam game installations between user accounts

Does anybody have experience with a similar setup?
Both my son and I have our own bazzite user accounts. I have a regular Steam account and he's got his own account to access the family library I set up. Installing games and playing game worked perfectly so far.
Now I tried installing games on a second ext4 drive that I added to the storage options in Steam. The idea was not having to install everything a second time, especially MSFS 2020. It works for me. His account can see these games as I hoped but when he tries to start a game Steam keeps validating and/or updating the installation and then stops before starting the game.
Is there a way to make this work?