This article lists the data types that ProBackup backs up for Slack and any known limitations.
What we back up
Users
Channels
Messages
Threads (up to 1,000 messages per thread)
Attachments
Direct messages that the connected user has access to
What we don't back up
Direct messages between other users
Channels the connected user does not have access to
Group membership and permissions
Workflows
These data types are not available through Slack's API. We will add them to the backup scope as soon as they become available.
Note: ProBackup can only back up data that the connected user has access to. To ensure full coverage, consider connecting an account with broad channel access or inviting additional team members.