AIUI, in addition to Manjaro and Ubuntu, quite a few distributions support strict confinement. OTOH some are Elementary, KDE Neon, Kubuntu, Mint, Lubuntu, Pop_OS!, Solus, Xubuntu and Zorin (a few are Ubuntu flavors, some derivatives that utilize the AppArmor patch set and others simply picked them up (they are self-contained after all)).
There have been updates since the update I gave not long ago. AppArmor 3 is in RC and will be uploaded to Ubuntu 20.10 (groovy) soon (days to week or two) with final coming before 20.10 is released. That obviously is only for one release of Ubuntu, but once that is done and we shake out bugs, etc, the idea I plan to propose is for snapd to vendor apparmor 3 sometime during the next development cycle (ie, sometime between November and April). This will allow using networkv8 that is in upstream kernels instead of requiring the network compat patchset.
Furthermore, we’ve reprioritized AF_UNIX wrt LSM stacking and are today actively working to land AF_UNIX in the upstream kernel ahead of the various LSM stacking iterations/pieces.