"If you are at risk for pelvic floor injury or suffer from weak pelvic floor muscles, avoid all exercises that place extreme stress on the upper abs. Avoid traditional sit-ups and crunches, bicycle crunches where both legs are raised at the same time, the twisting crunch, yoga or Pilates moves that involve raising the head off the floor at the same time as the legs, and gym machines that focus on the abdominals as an isolated movement. Exercises which are best for the pelvic floor muscles are those that keep your legs and head on the floor, or only one leg raised at one time, and lower abdominal exercises"
My physio told me more or less what I just pasted. Don't put two legs in table top but always leave one foot on the floor. the same with tapping one leg on foot at the time or raising legs.
This is why I suggested a session with private physio even if expensive to really guide you towards a proper form.
You need to lie on your back and put two fingers under your hip bone and feel under your finger just that muscle band contracting and going up and down until you lose it without contracting any other abs, so no bracing, engaging. It is very tricky to find.
The physio used an internal ultrasound to show me how the muscles were meant to move. It is not that simple at all to identify and isolate.
Stop doing crunches or sit-ups until you have at least done your research. There are a lot of video as well on this.
This one is in French but just watch to understand the posture you should keep while doing abs exercises www.fuites-urinaires-et-sport.com/astuce-abdos-danger/ . she makes it look very easy but it is pretty hard to keep the bottle stable.
My physio had me doing a lot of abs on my hands and knees (the cat position) and extending one leg-opposite arm.
IT was quite frustrating because I really always had all my life a six pack and I was used to very intense ab work so going to baby stuff was at first annoying, but it was my workouts that weakened my pelvic floor and giving births was just the last straw.