Disclaimer
Flatpak uses OSTree, like Fedora Atomic Desktops (Silverblue, Kinoite etc) and similar to BTRFS snapshots.
So many files are deduplicated and linked, not actually there
https://gitlab.com/TheEvilSkeleton/flatpak-dedup-checker
50GB without
31GB with deduplication
21,4GB with BTRFS compression
https://madaidans-insecurities.github.io/linux.html#firejail
https://seclists.org/oss-sec/2017/q1/25
https://cve.mitre.org/cgi-bin/cvekey.cgi?keyword=firejail
interesting, ill have to read more on these