When I first started cooking quick weeknight meals for my family, I ran into the exact same issue with cheeses turning into a greasy puddle in the oven. I tried several standard supermarket brands of cheddar, but they always separated because of the way they are processed. Then I switched to buying a basic block of whole milk mozzarella and grating it at home. It made a noticeable difference in the texture and overall quality of the baked vegetable dishes. While I still sometimes struggle to find older, sharper varieties that do not release too much oil when heated quickly in an air fryer, sticking to simple low-moisture blocks is generally a reliable approach for achieving a decent melt without all the extra additives.