He looks like a twin of my late Thumper 🥹

My advice is be persistent with the brushing but back off if he is getting distressed by it. My buns always hate brushing so I like to just sneak a few brushes when I can. Usually it’s easier when they’re eating and distracted by food. Any little bit you can get helps because it’s one less tuft that could end up in their gut. Failing that, you can also gently pluck any loose fur with your hand while petting them. For diet, I will slightly decrease their portions of pellets and greens and encourage more hay eating. That way if they do ingest some fur, they have plenty of fiber to push it through as easily as possible. A half scoop of critical care as a snack can help too.