Hmm. It’s kind of just a VPN. It tunnels your traffic and terminates it at some server with those IPs. It’s just that NordVPN etc make you share an IP with other users and don’t offer port forwarding. But the rest of Hoppy isn’t necessarily unique, it’s just a specific configuration of a VPN.
I rented a VPS and installed wireguard myself. And created the firewall rules to forward (some) incoming traffic to my home server. That’s the same thing Hoppy does. Just that Hoppy does the setup of the firewall and Wireguard for you.
But I’m not aware of any similar services that do it automatically. Maybe something like pagekite.net comes close.
So I don’t know if that’s the correct solution to what you’re doing but I’d say one alternative would be to rent any small server, install Wireguard both there and on the RasPi, connect them and configure Wireguard on the RasPi so all outgoing traffic goes through the tunnel. And then configure the like 3 firewall rules on the VPS to make it forward incoming traffic on all ports to the RasPi.