After changing Steam account, Game cannot play video. TV test pattern instead (Steam Family bug ?)

[nicolasnobelis]

Your system information

• Steam client version (build number or date): 1738026274 / Native installation
• Distribution (e.g. Ubuntu): LMDE 6
• Opted into Steam client beta?: No
• Have you checked for system updates?: Yes
• GPU: AMD

Steps for reproducing this issue:

1. As a family owner install proton (9 or experimental). Games are launching fine.
2. As the same OS user, change to another steam account, one that is a kid in the family.
3. Install a game.
4. Videos in game are replaced by a TV Video test pattern. Game is fine.
5. Manually using another Proton installed in the compatibilitytools.d directory (e.g. GE-proton) fixes the issue.

Maybe the family part of this bug is a red herring and only the multiple Steam accounts / single OS user part is relevant.