How to add Local Farm to permissions on Search Service Application

If the Local Farm (account) is not on the permissions of Search Service Application and users try to perform a search on any SharePoint site they will get an error and a correlation ID - something like below:

In ULS logs you'll notice the below error:

"SearchServiceApplicationProxy::GetUserPreferenceSerializeHelperForTenant–Error occured: System.ServiceModel.Security.SecurityAccessDeniedException: Access is denied."

There is a fix on this blog but it doesn't fix the issue (at least not in my case).

So the solution is to run the following powershell commands:

$farmID = Get-SPFarm | select id
$farmID

Copy the GUID returned from $farmID and go to Search Service Application click on Permissions and paste the GUID and grant Full Permissions.

And that will fix the issue.