I suspect the problem is that you are using the default Windows administrator profile and that directory EM_2 “doesn’t for some unknown reason have full write access”.
So try setting the backup target directory in eM Client to C:\Users\Administrator\Documents\eM Client and see if the backup runs.
If you still get access denied, then that means your current Administrator username you are using, “doesn’t have full full read \ write access to your profile Documents folder” and \ or sub folders, and you will need to “modify the permissions of the folders in the Properties \ Security tab”. See the below Microsoft links on assigning permissions and creating usernames etc.
Note:- Also you would normally login to Windows with either a “Local Profile username or a Microsoft Account Name” eg: Johnsmith or [email protected] and “then assign Administrator permissions to that”. So not normally login with the Administrator username.
(How do I set up user accounts and manage permissions in Windows 10 & 11)