Exercises you shouldn't do?

Hey guys,

I have stumbled across these videos https://www.youtube.com/watch?v=VKDlyhvZLaA and https://www.youtube.com/watch?v=wZcfJfn32oQ . I have done many of these exercises with better form (they often demonstrate an exercise with a rounded back, but then also reiterate that it puts a lot of pressure on the back even with flat/neutral back) and have rarely felt discomfort. I am curious do you feel this is something to be mindful of and have you had any problems that you could pinpoint back to any exercise (mentioned or not)?

I have experienced mild lower back pain from deadlifts a couple of years ago (I assume I was not engaging my core enough), but now I don't have issues with it. Also, my but wink (I didn't realize it had a name) is quite pronounced, so any tips with that are also highly appreciated.