I've got 5 glw pullets and 4 glw cockerels .. did you notice at hatch-3rd week the ones that were slower to feather in, and tend to have light/yellowish coloration on the wing area - those are the cockerels. At hatch, the pullets have a variable length feathering pattern on the wings - short, long, short, long, etc. The pullets have practically even feather patterns on the wing. short, short, short, etc.
From what I see of the pic, I'd agree with others, it's a cockerel
If this chick was 4 weeks old vs 3 would you still think cockerel? I ask because when I got them I believed them to be just a few days old but in the event they were a week old (feathering has matched them being around 3-3.5 weeks old) I’m curious what you’d think at 4 weeks of age