at the current moment I'm not quite 100% sure if this is a bug or a misconfiguration.

While connecting to
/server irc.hackint.org +6697
I get the error "Unable to connect to server (SSL certificate chain error)"

I am still using the old Windows 7, but I have already downloaded all root and intermediate certs from https://letsencrypt.org/certificates/ and have installed them as trusted CA.
But it's still not working.

Then I discovered this cacert.pem inside the mIRC folder. I have appended all downloaded letsencrypt pem certs to that file, restarted mIRC, but it's still not working.

Then I have downgraded from 7.64 to 7.61 but it's still not working (same error).
Before that upgrading I had Version 7.56 and THAT version was working with hackint.

Any suggestion?