Completely hiding Quick Access from the navigation tree in File Explorer can be achieved via the registry:

1. In the registry, navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer
2. Create a DWORD 32-bit value named HubMode and set its value to 1.

You may need to re-logon for the changes to take effect. You can also use group policies to apply this setting in a domain.