How to Delete All posts at once
To delete all posts:
Go to the Posts tab.
Filter accordingly by account, labels, and post type.
Keep in mind, Published posts cannot be deleted all at once, you have to delete them one by one.
Click on the three dots next to the "Grid View".
Choose Delete All.

Click Confirm, if you are certain that you want to Delete All posts.

To delete all posts for a specific social account:
Go to Accounts.
Select the specific social account.
Go to Settings > Delete all scheduled posts.

Keep in mind, this action cannot be reversed and the posts will be permanently deleted.
Updated on: 10/10/2022
Thank you!