Parallels Secure Workspace is configured to use built-in counter-based authentication.
Google Authenticator does not show a verification code (OTP code) for Parallels Secure Workspace.
An update published by Google for Google Authenticator.
Since the Google Authenticator update of the 23rd of May, 2022 (version 5.20R3), customers who use Parallels Secure Workspace's built-in counter-based authentication are no longer seeing codes. Even clicking the refresh icon apparently doesn't show a code.
There's no direct communication once set up between the Parallels Secure Workspaceappliance and Google Authenticator, this is an issue with the Google Authenticator app.
Mind that time-based authentication is the recommended option, as it is more secure. Switching to this mode implies that each user will need to go to the steps again to reconfigure their MFA. To switch to time-based MFA: Navigate to System Settings > Configure > User Connector: Multi Factor Authentication.
Another option would be to change to a different authenticator app that still supports counter-based authentication (mind that a lot of authenticator apps only support the more secure time-based authentication method).
Another reported work-around is to touch the account for a longer time in Google Authenticator, so the code is copied; and paste it in another application where you can see the code.