This is good to have and kept as default, something else should be figured out on how to make flatpak work.
Alpinelinux using the same kernel option:
But they say if you have flatpak permission issue just " add your user to the flatpak group."
https://wiki.alpinelinux.org/wiki/Flatpak#Permission_errors
Why turning off this option is not solution:
Workaround, worked:
[user ~]% sudo sysctl -w kernel.unprivileged_userns_clone=1
kernel.unprivileged_userns_clone = 1
[user ~]% flatpak install org.mozilla.firefox
Looking for matches…
Required runtime for org.mozilla.firefox/x86_64/stable (runtime/org.freedesktop.Platform/x86_64/23.08) found in remote flathub
Do you want to install it? [Y/n]: n
error: The application org.mozilla.firefox/x86_64/stable requires the runtime org.freedesktop.Platform/x86_64/23.08 which is not installed
zsh: exit 1 flatpak install org.mozilla.firefox
[user ~]% flatpak install io.freetubeapp.FreeTube
Looking for matches…
Required runtime for io.freetubeapp.FreeTube/x86_64/stable (runtime/org.freedesktop.Platform/x86_64/23.08) found in remote flathub
Do you want to install it? [Y/n]: y
io.freetubeapp.FreeTube permissions:
ipc network pulseaudio x11
dri file access [1] dbus access [2] bus ownership [3]
[1] xdg-download
[2] org.freedesktop.PowerManagement, org.freedesktop.ScreenSaver, org.gnome.SessionManager,
org.gnome.SettingsDaemon
[3] org.mpris.MediaPlayer2.chromium.*, org.mpris.MediaPlayer2.freetube
ID Branch Op Remote Download
1. [✓] org.freedesktop.Platform.GL.default 23.08 i flathub 164.6 MB / 163.8 MB
2. [✓] org.freedesktop.Platform.GL.default 23.08-extra i flathub 22.6 MB / 163.8 MB
3. [✓] org.freedesktop.Platform.Locale 23.08 i flathub 17.9 kB / 371.6 MB
4. [✓] org.freedesktop.Platform.openh264 2.2.0 i flathub 1.2 MB / 944.3 kB
5. [✓] org.freedesktop.Platform 23.08 i flathub 250.0 MB / 230.9 MB
6. [✓] io.freetubeapp.FreeTube stable i flathub 123.4 MB / 114.8 MB
Installation complete.
[user ~]%