man: note that DynamicUser=yes is incompatible with D-Bus

Due to policy checks against system users this cannot currently work, and it is non-obvious.
In the future it might be implemented if support is added to dbus-broker/dbus-daemon, e.g.:

bus1/dbus-broker#259

man/systemd.exec.xml

@@ -584,7 +584,8 @@
         <varname>BindPaths=</varname> and be careful with <constant>AF_UNIX</constant> file descriptor
         passing for directory file descriptors, as this would permit processes to create files or directories
         owned by the dynamic user/group that are not subject to the lifecycle and access guarantees of the
-        service. Defaults to off.</para></listitem>
+        service. Also note that using this option will stop the unit from being able to publish a new service
+        on D-Bus. Defaults to off.</para></listitem>
       </varlistentry>
 
       <varlistentry>