You can use a gps logging app (I use gps logger on android) to create gps tracks and sync them with your photos via the timestamp. Digikam has a tool for that built in, not sure what other software supports it.

This way I don’t have to manually tag every photo but instead only those where the gps failed because I was underground or where I forgot to turn it on

I believe the back to home VPN from MikroTik is also wireguard. At least it is on mine. No idea if you can use a different VPN solution with it.