Boot Loop after small drop.

Bootloops can be caused by almost anything, for starters try to boot the phone with just battery and display connected. If the phone boots fine that way then keep connecting other parts one by one until it starts bootlooping again to find the faulty part.

If this doesn’t work you could either assume it’s motherboard related and needs microsoldering work to get it fixed, also quite expensive but not 600usd expensive. Or you could also try to factory reset the phone to make sure it’s not software related if you dont care about the data on the phone.

Also if you’re not experienced in taking phones apart just take it to a third party repair shop instead of apple and let them do the troubleshooting for you, shouldn’t cost that much.