network-manager-wireguard/nm-wireguard-service.conf

<!DOCTYPE busconfig PUBLIC
 "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
 "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">

<!-- you have to be allowed to use the bus name "….wireguard"! -->
<!-- thus, copy the "<allow own_prefix='…'/>" and "<allow send_destination='…'/>" from below to a DBUS conf file -->
<!-- e.g. i copied the entire file to "/etc/dbus-1/system.d/nm-wireguard-service.conf" -->
<busconfig>
	<policy user="root">
		<allow own_prefix="org.freedesktop.NetworkManager.wireguard"/>
		<allow send_destination="org.freedesktop.NetworkManager.wireguard"/>
	</policy>
	<policy context="default">
		<deny own_prefix="org.freedesktop.NetworkManager.wireguard"/>
		<deny send_destination="org.freedesktop.NetworkManager.wireguard"/>
	</policy>
</busconfig>