You can’t spot reduce fat, so if you want to lose weight in your stomach you’d have to lose weight overall/lower your body fat percentage. Core workouts will just help you build abs/burn calories in general, which is helpful for body recomping and aesthetics actually so I would still recommend them, but the one you’re mentioning that builds a “boxier” look are those that target the obliques so you want to find one that doesn’t specifically. Some good core workouts are hollow body holds and butterfly kicks (which you can combine with crunches). Abs you can typically train with just bodyweight but there are always gym ab machines or just add ankle weights for resistance. Fat on stomach can also be cause of bloating sometimes too tho btw