As was mentioned in other posts, it is caused by the Nextcloud dbus service triggered by all programms that depend on GTK3/4.
A workaround is to disable the dbus service by overriding it, e.g. as described in [D-Bus - ArchWiki]:
$ mkdir -p ~/.local/share/dbus-1/services/$ cp /usr/share/dbus-1/services/com.nextcloudgmbh.Nextcloud.service ~/.local/share/dbus-1/services/$ sed -i 's|^Exec=.*|Exec=/bin/false|' ~/.local/share/dbus-1/services/com.nextcloudgmbh.Nextcloud.service
Don’t know how to make it work without needing to reboot though.