That is really strange, so the FQDN you have used for the 3CX installation is a non-3CX FQDN and you have used the same FQDN for Teams, correct?
If this is the case, can you go to https://www.sslshopper.com/ssl-checker.html and input the <FQDN>:5061, e.g. pbx.mydomain.uk:5061, and check if...