This article lists the data types that ProBackup backs up for Google Workspace.
What we back up
Gmail threads
All files stored in Google Drive
Calendars
Calendar events
Contacts
Contact groups
Which users are covered
The backup covers the Google Workspace data that the authorised account can reach. When you connect with a super admin account, that is the whole organisation. You can exclude individual users from the backup, which removes that user's Gmail, Drive, Calendar and Contacts from it.
Shared drives, shared folders and shared calendars are included when the connected account can open them in Google Workspace. Anything that account cannot see is not in the backup, which is the usual reason a shared drive looks incomplete.
What you cannot select per item
Within a user, the four data types are backed up as a whole: you cannot pick individual mails, files or events. Large Drive files are the exception. You can exclude attachments by size or by extension for the whole account, for example "mov" and "mp4", in https://app.probackup.io/settings/data-retention (See How to control your data storage.)