'Operation not permitted' error seen with private/var/db folders in BigSur

I am currently working for a Data Protection software solution. While backing up <private/var/db> folders using our product, there were issues with accessing <private/var/db> folders and backup of those fails with error 'Operation not permitted' .

I have provided 'Full Disk Access' permission to my application.

Error 'cannot open dir "." Operation not permitted' occurs for following folders.

(/System/Volumes/Data/private/var/networkd/db/):
(/System/Volumes/Data/private/var/db/appinstalld/): (/System/Volumes/Data/private/var/db/installcoordinationd/)
(/System/Volumes/Data/private/var/db/oah/)
(/System/Volumes/Data/private/var/db/lockdown/)(/System/Volumes/Data/private/var/db/DifferentialPrivacy) (/System/Volumes/Data/private/var/db/MobileIdentityService/)
(/System/Volumes/Data/private/var/db/searchparty/)
(/System/Volumes/Data/private/var/db/SystemKey)
(/System/Volumes/Data/private/var/db/DifferentialPrivacy)

(/System/Volumes/Data/private/var/protected/trustd/private/)

I have following questions:

1) What does above directory contains?
2) Why even with 'Full Disk Permission'( provided for my application), 'Operation not permitted' error is seen?.
3) Can these directories be excluded from backup?