Hey,
VPN's and port forwarding are both valid options.
Opening a port usually only benefits you, if you have a static IP or a dyn dns setup for the backup location.
Without that, I would go with a vpn.
There are a myriad of possibilities and if you ask 4 people, you will get 5 opinions.
If you want something easy to set up, you could take a look at Tailscale, they even have instructions on how to use them with proxmox [0].
Most of the selfhosted vpn's still need a lighthouse or something similar to be publicly accessible, which would mean that you have to rent
a vps. But if you want to go that route, I had very good experiences with nebula [1]
[0]
https://tailscale.com/kb/1133/proxmox/#enable-https-access-to-the-proxmox-web-ui
[1]
https://github.com/slackhq/nebula