If you're not looking to include all Users from a particular O365 Organization, you can follow the steps below.

1. Go to [Users] or [Groups & SharePoint]
    
2. Next, simply find the particular Microsoft 365 Organization you would like to exclude users from and click on the 3 dot icon.
   
   At this point you will get 2 options;
   
   [Pause this User or Group]
   Pausing Backups for this User or Group & SharePoint will stop backups from taking place in the future. The Backup Data will remain available and can be restored from the Restore Wizards. You will still be charged a monthly fee for this User. This feature is useful to retain backups of a User that has been deleted or archived in Office 365. To re-enable backups in the future simply choose to 'Re-enable Backups for this User'
   
   [Exclude User from Backups & Delete Backup Data]
   Excluding this User or Groups & SharePoint will stop backup and restore operations from taking place and delete all Backup Data. You will still be charged a monthly fee for this User. If you would like to Backup this User again in the future you may include it again but older backup versions will not be available.