If TPM firmware is up to date and Windows is up to date with at least September updates which addressed known issues with TPM not initializing, please don't disable modern authentication.
Check if machine is Azure AD joined, perhaps it was joined by someone else who previously signed into the machine and that users's key and cert is cached in the TPM.
If you check the ADAL logs, it should tell you the error we get back.
If you're AAD Joined per cmd->dsregcmd /status, then run dsregcmd /leave /debug, confirm it has left then reboot, have user sign in and test.
In addition, please ensure along with enableadal=0, there aren't any disable WAM or enableadal=2(for OneDrive) in place that will keep Office and Windows from behaving as designed.
Once Windows 10 client configuration has been ruled out, then MSFT can assist further by looking at trace or otherwise.
Finally, if you go to help and collect diag logs in Outlook clients, it'll capture ADAL and TPM logs along with reg key information in a zip file that you can review to troubleshoot step by step based on Office sign-in workflow.
A workaround should not be needed for issues like this.