NetDrive uses different credential for each drive. So
1st drive : uses credential of sysadmin
2nd drive : uses credential of user B
then NetDrive requests to Nextcloud server with different credential.
Connect Nextcloud with sysadmin account only(just one drive).
And User A(who has Folder 1 access permission on Nextcloud) access NetDrive with SMB shares that connected with sysadmin account. Also User B access same drive with User A.