I see Kase's request that Yamada not wear those clothes in fireworks festivals in Tokyo as possibly coming from a place of jealousy, but also coming from a place of concern. Yamada's shown herself to be naive about guys, in the chapter where they're at the swimming pool and the college men are trying to hit on her before Kase rescues her, she both misunderstands the situation, doesn't know how to handle it, and doesn't like it (https://dynasty-scans.com/chapters/kase_san_ch10_1#26). Kase is presented as much more worldly than Yamada, and thus is protective of her. But there are many ways to view it. I'm opting for Kase just giving advice to keep Yamada out of a situation Yamada would find awkward VS Kase is controlling.
Granted Kase's reaction isn't the most woke take about this type of situation (feelings of concern over a partner's attire), but this comic is meant to be lighthearted and fluffy - a romcom where the plot is driven by simple misunderstandings between well-meaning characters, not a treatise on healthy relationship dynamics between adults, frankly how little they honestly talk about what's bugging them would be a huge red flag in a real relationship (but it fuels most of the comics).