IIS 6.0 went EOL in 2015 and is from the Windows Server 2003 days. 6.0 has SSL support but the cipher set is likely so old that most modern browsers would probably still reject it. A reverse proxy like nginx might be an option but the windows binaries are quite limited in capability. Apache would be more likely to work, though even that might still be tough to get running without using an old version.
In theory newer versions of IIS still support the classic asp.net that the site seems to use so it might be possible to migrate to Server 2019 or 2022, but legacy migrations are always a challenge. That's probably what I would try if it was up to me.
(Long-time member with a new account because the password reset SMTP config isn't working)