This is just for information for anyone who has the same error message, when they try to disconnect the Security Key from a user's record:
You don't need to try later. It wont' work. Simply reaise a ticket with Salesforce to remove it for you. This has been identified as a "bug" and Salesforce confirmed to me that it will be fixed with Winter 23.
"Hello Krasi,
I checked internally with the product team and from the internal case, I see the resolution to this bug is in progress and is scheduled to be released with our 246 i.e. Winter 23 release.
We sincerely apologize for the inconvenience. "
Hope that helps to anyone as there is no documentation currently released by Salesforce in regards to this particular issue.
Jonathan Fox (Cooper Parry) 
Forum Ambassador
Hi there!
You've posted this as a question rather than a post - is there anything that you need help with or did you just want to share this for others to know :) ?
