FileVault - vile fault!

How do I disable FileVault in my new MacBook Air (Catalina 10.15.2)?

I go to the FileVault tab in System Preferences / Security & Privacy, click on the Turn Off FileVault button, nothing happens. Then I go down to the "Some users are not able to unlock the disc." and click on the Enable Users button, and still nothing happens. I do this in my User account and Admin account.

I have my long FileVault password at the ready...

Any suggestions?

Thanks.