Setting up Managed ID with Apple Business Manager (ABM)

See Create Managed Apple IDs in Apple Business Manager https://support.apple.com/guide/apple-business-manager/create-managed-apple-ids-mdm1c9622977/web

Your problem may be that you are trying to use an Apple ID that is, or was, in some way, associated with another Apple ID of yours (e.g., as a reachable at email address or a notifications email address). Note that you can't use such an Apple ID for an uncertain period has passed --sometimes reputed to 30 day and sometimes 1 year. Also, I have seen that you never can use such an email address again (e.g., if the account was deleted). The last two times I saw someone claim a time period it was “up to 30 days.” I believe that up to 30 days is the current answer. 

But, you can contact Apple support using the options below to check out the currently quoted wait period.

Apple telephone support https://getsupport.apple.com/caller=kbase&PGF=PGF63005&category_id=SC0245&symptom_id=23362 

Be patient. Sometimes Apple phone support is not available.

Apple ID Support https://support.apple.com/apple-id

Apple Support Twitter  https://twitter.com/AppleSupport There may be an hour or so wait.

Apple ID account security for country-specific andregion-specific help https://support.apple.com/en-us/HT204169

Get Support: We’re here to help https://getsupport.apple.com/. Go through the options to find the best support option.

If you are using what has been your Apple ID, according to the screen shot, you need to change the email address to a new address.

Note the restrictions in the article.

Apple ID Name Change.        

 What to do after you change your Apple ID or password - Apple Support    I suggest doing this before you change your Apple ID or password.

Apple ID -Two-factor authentication          

You might want to contact Support to make sure you follow the correct procedures.

Get Support for Apple Business Manager.