Q: is a VPN the only way to access MinimServer from outside the local network?

[dukdukgoos]

I assumed VPN would work but it doesn't, apparently there may be some complicated hacks to get UPnP to work with certain VPN mechanisms (OpenVPN) but I didn't explore further as it seems to be bleeding edge/buggy (plus I don't currently use OpenVPN).

I'll look into BubbleUPnP Server though, thanks for that advice!