Support

It's not the host's CA bundle because Joomla! uses the composer/ca-bundle dependency to isolate itself from the host's CA root, using the cacert.pem file bundled with this dependency. The fact that you have the same problem, at the same time, with three different versions of Joomla which use different versions of this dependency when nobody else using a different host, including myself, can reproduce this tells me that the problem is neither in this file, nor Microsoft's certificates.

If I had to guess, your host has very recently made changes to their transparent proxy's configuration. Something they did seems to break the TLS handshake, or inject its own TLS certificate which is of course not signed by any public Certification Authority. Ask them to assign your case to an actual server engineer who can troubleshoot it properly.

It's one of those things that do happen, and usually the frontline support agents don't know about. Once you get the engineers involved someone very quickly goes "oh, shoot…". :D