Starting from the end: From your description My first guess is that you have local issue with the installation.
If I understand you correctly then this issue is only from specific machine (as you mentioned that other "can connect without issue").
(1) What do you mean
"in both SSMS 18.2 and 18.12.1"? Do you have both version on the same machine? This is not supported. If in someway you got this scenario then you should uninstall all and have a clean installation of the latest version (hopefully the uninstallation will not leave something behind)
(2) Your best option might be to uninstall it and re-install, but before you do so,
(2.1) Try to use the Azure Data Studio (without installing anything). Check if this connect the server well
(2.2) If this is not a production machine then you might want to tests SSMS 19, which can run side by side the SSMS 18. This is a huge advantage which let you test it and check if your issue continue on SSMS 19.