There's a troubleshooting guide for FME Server specific to login issues, did you find that one?

Looks like you browser cannot access the necessary javascript libraries that are part of the FME Server installation. Verify your network permissions/firewall and any 3rd-party browser plugins (e.g. adblockers, etc).

Also check the Tomcat logs for any errors on the server side.

Checked the log files and done the troubleshooting method mentioned above. Yet, I face the same error. Attached the log file for reference. Any thoughts on this would be appreciated

fmeserver.log file

My recommendation would be to escalate the issue through your FME reseller/partner.