Yes I did try creating a file. This is what I have tried.
1. I gave Full control to Qlik service user and created a file while logged in as Qlik service user.
2. I gave "Everyone" full control and then creating a file using while logged in as Qlik service user.
3. Used IP address as accessed folder path e.g. "\\10.0.0.1\Shared" then I thought it might not like IP addresses as I use machine name when I have the shared folder on the same machine e.g "\\WIN-638HFJ\Shared". So I also tried using the machine name when the machine was on a domain e.g. "\\fileserver\Shared"
Neither of the above cases work while the shared folder was on a different machine. However in all the cases I was able to open the shared folder using windows explorer and create a text file and write to it while logged in as the service user.
Also again it works if the shared folder is on the same machine.