Is it similar to the case of abs fat, in which Doing crunches and
other abs exercises will not burn belly fat, but just build your abs
Yes, just like abs workouts, you will not spot reduce fat. Fat is loss over your entire body when you are at a caloric deficit. There are exceptions, but generally speaking this is the only way to lose fat.
If you are exercising and gaining muscle while at a caloric surplus, the fat does not go anywhere, it stays on your body. In fact, you will actually gain some fat. The proportion between fat and muscle gain will depend on your caloric intake and activity level.
Likewise, when losing fat, you also lose some muscle. The amount depends on how much protein is consumed and activity level.
Now, if you consume as much calories as you burn, your weight will remain stable.
Where your body will store fat fluctuates a lot between individuals, but will mainly be stored in areas where there is a lot of space for them to be packed in. (Butt,Thighs,Belly, Breasts) You cannot control this and your body will decide what is the best place to store it.
My question is , when building muscles in a specific position of the body (let us say the butt), what happens to the fats present in this position?
You're asking this question, so I will assume you are new to weightlifting / exercising. You will lose fat (if overweight) as your body will use a lot of energy while you progress through your beginner's gains*. Realistically, your fat will either remain on your butt if you stay at maintenance caloric intake. Your butt look and feel a lot firmer however, seeing as your muscle-to-fat ratio will be higher.
*As long as you eat at your current maintenance or a caloric deficit