So it’s not impossible to forget or lost a VPN password and Windows doesn’t tell. I was looking for it in the Windows password manager - there are credentials for networks, websites (if you, for some reason, use an Internet Explorer), shares, DAV and so forth.
VPN credentials are not stored there, though. Not really sure about this, but I assume it’s because the RDP is much more older than the password manager. Who knows.
Anyway, there’s dialupass. You just basically run it and it shows all the stored VPN credentials with readable passwords. Neat.