Select specific fields in Eloquent eager loading not working

Maybe selecting the fields like this works out:

$notifications->load('user:id,name,email');

What you are trying is designed to add constraints, not to select some fields

Just needed to add the primary key column and that worked fine.

$notifications->load(['user' => function($query){
    $query->select(["ID","name","email"]);
}]);

This way any constraints can be added to the query.