You statement is correct: "Link the new GPO policy (if not done already) to an OU with a user account that can be used to test this policy. This user must log on to a Windows computer to allow proper processing of this policy."
This is distinct from configuring the permissions on the GPO. Both conditions must be satisfied
To implement this, follow https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-r2-and-2012/dn789193(v=ws.11)#how-to-link-group-policy-objects
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hth
Marcin