Deny access to Veyon if a user is not listed in a local group

[cesare]

Hi,
I've been using Veyon for years in my pc labs.
On the teacher desk before only teachers were allowed to access the pc (AD authentication). Now we are switching to GCPW (Google Cloud Password for Windows) and this now allows all our users to access the teacher desk PC.
I wish I could stop users not belongings to a local group of users to access Veyon, but with no luck since now.

Users who access with GCPW on a pc are created as local user so I guess that if I can put the ones I want to access veyon in a group I could filter them.
I've tried with "Access Control" > "Restrict access to members of specific user groups", selected my local user group and tested and the tests works well.
But it doesn't work. I mean, if I login with a user not included in my "veyon" group it still can access veyon and use it with no problem.
I followed this: https://docs.veyon.io/en/latest/admin/reference.html#access-control

i read at the end "Do not forget to transfer the configuration to all computers afterwards."
I've tried, but obviously local group is not present.

So, what am I doing wrong?