Is it effective for treating melasma, even on cheeks that have darkened after sun exposure?

Since spending a lot of time outdoors during the summer, the color on my cheeks has become duller than before, and the light brown areas seem more visible, so I am looking into melasma treatment. I usually apply sunscreen, but I am not able to reapply it frequently while out, so I suspect that I may have been affected by UV rays.

I didn't used to be very concerned about it, but recently, even when I wear makeup, it feels like my cheeks aren't completely covered up.

Can I expect melasma treatment to be effective even on pigmentation darkened by UV rays?

I am also wondering if I need to be more thorough with sun protection while receiving melasma treatment.

I would also like to know what lifestyle habits I should pay attention to besides sunscreen to prevent melasma from darkening again after treatment. I want to maintain the results for a long time rather than just seeing a temporary lightening.