Is this possible? can i host steam games with that? say i setup a vps server based in frankfurt/germany… i have an open nat but my ISS blocks p2p 
Yes you can host steam games on a vps.
I host a palworld server, sons of the forest server and a Minecraft server currently on a vps.
Yes, a VPS in Frankfurt would give you a German IP and bypass your ISP’s restrictions on P2P. Just make sure the VPS has enough resources (CPU, RAM, bandwidth) to handle the game hosting and that the server allows the required ports for the game to work.
a vps server adds too much ping?
Same ping as steam online servers. If you play online you will always have a higher ping than playing offline.
like should i expect the same amount of ping from a frankfurt server of vpn service?
how about NAT type though, since you can host games and people can join you is it OPEN nat?
Depends on the vps which profile is used but there shouldn’t be a problem to open any nat port you need. Just need to configure it on the vps. There should be tutorials for it on the vps provider homepage