it is exactly what I think it is. you can use your own certs

I think thats up to debate.

Wikipedia says:

A virtual private network (VPN) is an overlay network that uses network virtualization to extend a private network across a public network, such as the Internet, via the use of encryption and tunneling protocols. In a VPN, a tunneling protocol is used to transfer network messages from one network host to another. Host-to-network VPNs are commonly used by organisations to allow off-site users secure access to an office network over the Internet. Site-to-site VPNs connect two networks, such as an office network and a datacenter.

So my argument is, if it is not used for private communication between multiple clients, it's not really a VPN.

Lets say, we both connect to the same Proton VPN server - our computers would not see each other and would not be able to connect to each other via that service. It has effectively the same function as a proxy - making your public internet traffic appear to come from the IP of the proxy server instead of your home IP.

Whereas if you set one up yourself with openVPN for example, we could make it so that we both get a VPN internal IP that we could use to directly connect and idk, play minecraft or something. Instead of connecting through the public internet, we would connect through a virtual network that is private for the two of us.

Oh I forgot to say: I have crowdsec on the VPS in front of frp and traefik on the server at my home, where I add all the modules I want.

frp just pipes all the packets through transparently.

But yeah, same thing, should work the same and there are dozens of ways to set that all up.

Hell the ability to access the internet via the tunnel, called Split Tunneling, is also controllable.

It’s that ability to control where the tunnel terminates that allows consumer VPNs, like Proton, to be used the way they are.

you can do the same split tunneling via proxy servers

while private individuals absolutely do use VPNs as an ersatz replacement for Proxy Servers they are nowhere near the whole use case for VPN

I agree. That also means that for certain usecases they are equivalent. It's sometimes worth checking all options to find the best one for that specific case.