WireGuard itself only operates on IPs (NIC interfaces can have an IP, but not an FQDN) hence in the current ConnMan-VPN implementation this is also a hard requirement. The wg-quick script that some WireGuard implementations use to create and tear-down WireGard interfaces has the advantage of being able to resolve an FQDN to an IP address before creating the interface. I haven't tried wg-quick on LE for aeons but it probably works, or you can create your own up/down scripts for systemd to make connections if you like; WireGuard support is in the kernel and making connections is not tied to ConnMan. The advantage of using ConnMan (and reason our default support uses it) is you can see and enable/disable connections using the LE settings add-on in the Kodi GUI.
thank you for all the info and for sorting me out. I hope someone else also benefits from this info