i would say tentatively no if you do them with 100% proper form, lots of "this exercise is bad for you!11" tends to be sensationalized clickbait with gimmick solutions
however i havent read about sit ups so idk i could be talking out of my ass rn
the problem people say is with your lower back i think but there are other exercises you can do for abs that arent sit ups. one way is to do exercises for your transverse ab muscles cos then itll have make abs look more defined too
however i havent read about sit ups so idk i could be talking out of my ass rn