Hi Zuuber,
You may need to include Loopback processing in your GPO. This policy directs the system to apply the set of GPOs for the computer to any user who logs on to a computer affected by this policy. Check Loopback processing of Group Policy.
Basically, you need to create your GPO with the Computer Configuration policies in it, including the Configure user Group Policy loopback processing mode under Computer Configuration / Administrative Templates / System / Group Policy.
If you just need to apply it to a particular set of users, you can use Security group filtering. Check Assign Security Group Filters to the GPO
I hope it helps.