Iphone Master Reset
Can anyone take the backup of the iPhone after the factory reset?
iPhone X, iOS 14
If you backed up the phone to iCloud, the backup can only be accessed, if you know the Apple ID and password, that has been used, to log into the iCloud account.
Erasing the phone will also erase the connection to the Apple ID account.
Check this article as well:
What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support