Устанавливаю Brave через flatpak, дистрибутив Sisyphus. При запуске получаю окно с ошибкой, текст ошибки такой:

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Your Flatpak version does not support a feature needed for this application to run.

This generally happens when your distribution has unprivileged user namespaces disabled, or your Flatpak version is older than 1.8.

If the distro you are currently using is Debian or a derivative (Ubuntu, Mint, etc), you can run the following commands as root (you can enter a root shell via sudo -i):

dpkg-statoverride --update --add root root 0755 /usr/bin/bwrap
echo kernel.unprivileged_userns_clone=1 > /etc/sysctl.d/50-bubblewrap.conf
sysctl -w kernel.unprivileged_userns_clone=1

Enabling unprivileged user namespaces on other distros

If you installed a "hardened" security kernel, these also usually disable unprivileged user namespaces. They can be re-enabled by running the following as root (you can enter a root shell via sudo -i):

echo kernel.unprivileged_userns_clone=1 > /etc/sysctl.d/50-bubblewrap.conf
sysctl -w kernel.unprivileged_userns_clone=1

If ls -l /usr/bin/bwrap contains rws, then bwrap is also setuid. This can be removed, if present, via:

chmod u-s /usr/bin/bwrap

However, note that the permissions may be overridden on the next update of your distro's bubblewrap package.
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P.S. Инструкция не помогает, ошибка та же.