I have a problem with Wireguard&OpenVpn.
I have this system, FritzBox 6591 Cable for the Internet and a FritzBox 4040 with OpenWrt for the Home. The systems work fine.
I have OpenVpn for NordVpn to maintain the security at Home.
I have Wireguard for VPN with my iPhone connected on the router.
Both systems work well when I connect them separately. But when I connect OpenVpn, the connection Wireguard and mein iPhone goes down and when I disconnect OpenVpn the connection works well.
What can I do to have Wireguard and OpenVpn working in the same time?

NordVPN installs a new default gateway when you connect. So outgoing packets of WireGuard go via NordVPN instead of ISP.
One simple solution would be to disregard the default gateway from NordVPN and use source based routing for the LAN hosts that must go through VPN.

You have 3 options:

  1. mwan3 package
  2. pbr package
  3. a set of rules/routes.

How do I configure it correctly?

Better do it with the pbr, it is more easy for newbies.

Nothing, because WireGuard uses UDP only.

tutorial with Mwan3. I have install the pack LuCI-app-Mwan3

Make a rule for the lan IP addresses to use the vpn only policy.
Make sure that you don't pull routes from the vpn first.