Last year Apple forced the industry to only accept TLS certificates with validity up to maximum of 398 days. This is documented in HT211025 article. However there is a note explicitly excluding the certificate issued by an internal CA:
This change will not affect certificates issued from user-added or administrator-added Root CAs.
Because of this I assumed I could get away with 3 year validity for a certificate issues by our new internal CA. Turns out I was wrong.
Safari 14.1.1 refuses to connect to a site with freshly issued 3-year TLS certificate. So does Chrome 91 but it is more informative about it and presents an error message:
Previous change of TLS certificate requirements from 2019 described in article HT210176 article limits the certificate validity to 825 days. There aren’t any exception listed in this articles. Would Safari and Chrome trust certificate with 2-year validity?
Yes. Both Safari (14.1.1) and Chrome (91) in macOS 11.4 accept the 2-year certificate signed by internal CA as secure.