You have a short circuit on the logic board. This is a common problem, but it doesn’t have an easy solution. There are tons of videos on my YouTube channel (iPad Rehab Microsoldering) showing identifying and solving short circuits. On a Xsmax there’s no “common spot” and it could be between the double stacked layers of the logic board. This is every microsolderers favorite problem to solve—once you identify the cause of the short that is usually the only thing wrong. I’d find a local microsolder who has a microscope and thermal camera to help you find your short.