Users who upgraded to Ubuntu 25.10 have encountered issues installing or updating Flatpak packages. This problem is caused by changes in the AppArmor rules applied when running the fusermount3 utility. Due to incorrectly set access rules, attempts to install or update packages using the flatpak utility result in an error message about the inability to unmount the directory /var/tmp/flatpak-cache-*.
The problem has been assigned a critical level of importance. Currently, an update for the AppArmor rules is being prepared and is under review. Until it is ready, a workaround to temporarily resolve the issue is to disable the AppArmor profile for fusermount3.
Source: opennet.ru
