Safari can't log into Apple websites (discussion forums, iCloud, AppleID, etc) on High Sierra

I'm restarting this thread that hasn't been updated since March 2020, saying apple developers were aware of the problem and "working on it": https://discussions.apple.com/thread/251163073?page=3

For a while now from Safari I have not been able to log into Apple websites that require a login. These forums for example, or iTunes Connect, or developer.apple.com. It says that Safari cannot open the page because it can't establish a secure connection to the server "idmsa.apple.com".

So really, High Sierra doesn't work with Apple's own sites? That cannot be true. There would be some mention of it online, I would think? I can't upgrade to Catalina. I might do Mojave, but at this point I just want to leave this computer running High Sierra to maintain the highest software compatibility.

I can use Chrome to access this developer forum and the other sites, but I find it super ironic that Apple themselves cannot help me to access their own sites from their own computer using their own OS which is only 3 years old.

Anyone have any suggestions on how to fix this problem without updating the OS?

Anyone have High Sierra and able to access these forums, iTunes Connect, or developer.apple.com?

Thanks!