Secure folder

You cannot backup for the secure folder the reason is due to security and encryption provided by Samsung Knox, which ensures that Secure Folder data is isolated and protected from external access, including through PC backups.
But u can backup using Samsung cloud

We’re truly sorry to hear about the inconvenience you’re experiencing, unfortunately, the Samsung Secure Folder does not support backup functionality. In this case, the alternative method involves saving your data to the phone gallery and then proceeding to back it up from that specific location. While it may require an additional step, ensuring that your important information is stored in the phone gallery allows you to implement backup measures effectively.

To move out of a secure folder:

Select file(s) > Tap [︙]
Tap Move out of the Secure Folder.
The moved file(s) will disappear from the gallery in the secure folder.