Some options you might not have thought of. Unfortunately, most of these mean you need to have access to something in the same local network.

• Wake on LAN. If you can find the MAC and have inbound port forwarding, you can send a magic packet with no further authentication. I’m guessing you don’t have any open ports hence tailscale.

• Lights-out management (iDRAC etc.) on the server motherboard if you’re using one.

• Similarly, web interface for a UPS or PDU.

• Might be able to get the power company to do a disconnect and reconnect, but that’s a stretch.

• Get someone with access to the property to be your hands.

Is your present ISP the only option for fibre in your area? Most ISPs here in NZ will give you a public static IP for a $5-10 monthly charge or sometimes $50 upfront. That’s easier and probably cheaper than dealing with a VPN or other remote access, and doesn’t impact performance.