See https://matrix.to/#/!RfXaBjokqHAbzZrgHz:matrix.org/$Xm7xnquFI5NTtTJzMCVk6chyqwoRTFcoqTah9wdXG1U?via=matrix.org&via=gnome.org&via=kde.org
and search the web for "X-GNOME-UsesNotifications=true".