as suggested by the forum, I you would like to keep any data that has been deleted on Office 365 for a maximum of 30 days and at the same time keep user data forever that has not been removed yet from Office 365
Snapshot based will remove data from the backup if it's removed based upon the defined retention.
For now, this option isn't available as we don't have a "move deleted O365 data" option yet if I understand your request correctly.
Is it correct you want it as described below:
a) Keep all O365 data in the backup
b) IF O365 data is removed, "move" the deleted data to a separate repository or mark it in the backup file (sort of temporary archive?)
c) Remove the deleted data after 30 days