What foods should I focus on to lose weight but build muscle?

To the extent that you, based on current weight, age, gender, and training history, can achieve weight loss and muscle gains at the same time, eat slightly below maintenance calories, get plenty of protein, and pursue a progressive resistance training regime. Allow for rest days, which is when your body actually builds muscle.

The specific foods you eat within the framework of small calorie deficit and sufficient protein (and sufficient means more than your maintenance amounts, so you have some to spare for building muscle) don't matter that much, although you may find it easier if you get a fair amount of your protein from animal sources (fish + eggs if you eat them).

Yes, I'm not giving you any specific numbers. You didn't give us any.

Foods that add up to overall good nutrition, especially but not exclusively ample protein: Enough protein, enough healthy fats, plenty of varied, colorful veggies, fruits and whole grains for micronutrients and fiber. It should be very possible with fish and high-quality plant protein sources. (I'm vegetarian, don't eat fish, do eat dairy. I have no special problems gaining strength/muscle when I put in the work. I have no problem getting ample high-quality, bioavailable protein that's reasonably balanced in essential amino acids. I'm getting those other nutrients reasonably well on average, too, of course.)

Depending on how you prioritize your goals, and what your body weight is currently, your best bet would be either a small calorie deficit to gradually lose body fat that way, or maintenance calories to stay at constant weight and let body fat provide part of the fuel for muscle growth. A larger deficit will trigger faster fat loss, but at the cost of slower or no muscle gain.

Muscle gain is more about the strength program, and how faithfully you follow it, than about the meal plan, assuming you get at least minimally adequate nutrition. The strength exercises you perform will influence where on your body the gains happen, along with your genetics.

Neither exercise nor dietary style can meaningfully influence whether you lose body fat on particular body parts vs. other body parts. There's no way to spot reduce fat: Your body will choose where the fat will deplete first, probably mostly based on genetics and sex hormone profiles (natural or medical).