Have your tried having a look at the home button flex just in-case you have caused any damage to flex while opening it happens to the best of us sometimes. If not I would try a different charge port see if that solved the issue, then I would try change the battery to see if that made a difference always rule out parts before you look into anything to deep. If after all that nothing works I would then start to have a board level work, such as reading diode values ect.
You might have already done this but, have you tried sliding them little side bits up as the arrows are pointing up and it looks as if there is a gap there for this. Not 100% Maybe wrong. Please comment how you have figured this out if you get this so others can see this if they have the same issue.
This could be hard to say mate, Random reboots can happen because of firmware issues, but can also happen due to some app you may have installed that is making the system unstable, or perhaps some bad bit of data that is in the systems cache.
I can agree that the face-ID will not work but I couldn’t imaging the front facing camera fully not working if you have another camera try and swap it to see if that makes a difference or try your camera in another XS Max if the camera works in another phone you have a issue with the logic board, but if a new camera works in your phone then it is just the camera that is damaged. Hope this helps.
Just for the sake of testing mate, I would one by one start adding the old parts back into the board until the error was cleared, use the process of elimination to try and work out what part is causing the issue. If you find the problem is with the new WiFi card that you purchased I would then place the WiFi card into a different system to make sure that card worked properly, for all you know they might have just sold you a faulty part.
Hello Mate, Personally I would attempt to find a thin Nail or something sharp with a point on the end. Then i would add some acetone / Strong Nail Polish Remover to the effected area then I would attempt to pick the remaining glue out using the acetone to help loosen / soften the glue. After a bit of work hopefully you have a nice clean screw head in which you can attempt to remove again.
They may be a possible chance that there could just be lots of dirt / lint inside of the buttons making the connection weaker or making it hard for the button to contact. Try cleaning them with some IPA, or try get hold of some replacement buttons and swap them out see if that helps you.