You could’ve scrolled down to the bottom, clicked on “Links,” then clicked on the repo link
The repo has instructions to install a Snap or build from source. If you build from source, it looks like you should download an archive from the releases page rather than just pulling from master.
Do you only experience the 5-10 second buffering issue on mobile? If not, then you might be able to fix the issue by tuning your NextCloud instance - upping the memory limit, disabling debug mode and dropping log level back to warn if you ever changed it, enabling memory caching, etc…
Check out https://docs.nextcloud.com/server/latest/admin_manual/installation/server_tuning.html and https://docs.nextcloud.com/server/latest/admin_manual/installation/php_configuration.html#ini-values for docs on the above.