Hi ,
Welcome to our new Microsoft Q&A Platform.
https://learn.microsoft.com/en-us/windows/win32/nps/ias-radius-authentication-and-accounting
According to Microsoft official document, NPS fully supports RFC 2865. Based on my research, RFC 2865 should be version 2.0 and RFC 2138 should be version 1.0. Radius version 1.0 limits authentication to 16 character passwords, while radius version 2.0 supports more than 16 character passwords.
For more details about RFC 2865, please refer to the link below:
https://tools.ietf.org/html/rfc2865
Best Regards,
Candy