Yes. You’re supposed to. They say there can be tiny fractures that can make the seat not safe in another accident. Also if you have insurance they typically cover the price to replace seats. Look in your car seat manual. Most, if not all, of them say to replace after any accidents
You don’t have to replace it. Stop looking to Google for everything
I believe you only need to replace car seats in moderate / severe crashes not minor crashes. A minor crash means no visible damage to vehicle, you both drove away from the scene, no airbags, no injuries, etc.
Are you calling insurance about this incident? They usually reimburse you for it. If you do decide to replace it anyways.
You can replace it and if in the US and going through your car insurance they may actually reimburse you for it. Did you file a police report?
No I wouldn’t. I got rear ended on the freeway. I was hit at around 30m/h. I still have the same seat.