Zrythm Flatpak doesn't list installed plugins

Zrythm doesn’t detect my plugins.
In the Setup under plugin path I entered:
/usr/lib/vst
/usr/lib/vst3
/usr/lib/lv2

Those directories aren’t accessible from Flatpak sandboxed apps. See Scanning for Plugins - Zrythm 1.0.0-rc.1 documentation

You need to install plugins you want as extensions via flatpak. See the “add ons” here for example: Install Zrythm on Linux | Flathub

Most ot the listed plugins aren’t available as flatpaks.
Or is there a special (flatpak) command on how to install them to make them available in Zrythm?

What do you mean by “listed” plugins? If a plugin is not available as a Flatpak addon based on org.freedesktop.LinuxAudio.BaseExtension , then it won’t work (there are some hacks but you are on your own there).

If you can’t stay within the Flatpak ecostystem, then my suggestion is don’t use Flatpak at all, use the official installer version or build Zrythm yourself.

If you mean Flatpak addons it looks like you can install them via your local Flatpak manager.

I found this in GNOME Software for example: