An old Microsoft VPN protocol, still offered by some consumer routers and older firewalls because it is trivial to configure and supported out of the box by most operating systems. That convenience is the only remaining argument for it.
Cryptographically broken. Its authentication can be cracked in hours regardless of password strength. Treat a PPTP VPN as providing no confidentiality and replace it with WireGuard, OpenVPN or IKEv2.
An open PPTP endpoint offers a false sense of security, because its encryption is broken rather than merely dated. Replace the VPN instead of trying to harden it.
The port scanner will tell you whether 1723 is reachable on a host you control. Checking from outside your own network matters: a port can be open on the machine and still be blocked at the firewall, and it is the view from the internet that decides whether anyone else can reach it.
Only scan hosts you own or have permission to test.