Problem with different Apple ID (iTunes Store etc.) and iCloud accounts

I have had different accounts/logins for my Apple ID and my iCloud account for years without a problem but on a new (2020) iMac running Monterey there is now an Apple ID section in System Prefs but no longer an iCloud section.

If I use my normal apple ID (to have access to software purchased and updates etc.) I get an empty iCloud drive. If I add my iCloud account in the Sharing section, I can see the account but it says it's not my "primary iCloud account" and cannot be used for iCloud Drive, etc.

Does anyone know what needs to be done to resolve this without messing up either existing account?

Many Thanks!