[zaisty]

Question is where to put aacs/KEYDB.cfg file and folder in Kodi Flatpak release? I need it to play my blu ray's.
On ppa version of Kodi everything works because it uses system /.config/aacs... folder.

[DaVu]

And what stops you placing that file there as well and make that folder accessible to Kodi-Flatpak by using "overrides"?

flatpak override tv.kodi.Kodi --filesystem=/home/<your_user>/.config/aacs/

After the command above, Kodi should be able to access that folder.