Hi! I haven't used Wireguard so maybe this is not of any use to you....
However I set up 2 OpenVPN servers on my AX88U. I can connect to both of them through my phone using LTE, through my laptop using LTE or through my laptop on any other wifi LAN. It isn't that fast for large scale file transfers, but works well enough for management purposes. I can access all devices on my LAN (including a QNAP NAS) as well as my secondary back-up QNAP NAS on my brother-in-laws LAN.
I have been considering trying Wireguard, but since I got OpenVPN to work 2 years ago, why change?
It took some fiddling to get it to work, but the most important thing was the IP address ranges on the network I try to access. They need to be completely different.
For example:
My local IP address range is 192.168.5.1 - 192.168.5.200
My local IP address range in Spain is 192.168.10.1 - 191.168.10.200
My brother-in-law's local IP address range 10.2.1.1 - 10.2.1.200
Those address ranges are just examples, not the real ones.
If we have the same local IP address ranges in the two LANs we try to connect it will not work.
When I have started the OpenVPN client outside of my home, I can access a device on my private LAN using it's local IP address.
