n3DSXL has gave up on life

Clues of DeviceID are signed right in the legit tickets for eShop purchased titles, and the OTP is part of the bootrom(?) found on the ARM CPU.

It's why someone can't just dump their legit tickets, publicly upload them somewhere like to that ticket site, have others install the tickets on their 3DS systems, and then they (re)download your games. Nintendo would be suspicious from that (1) am714's copy of Pokemon Sun has been requested to be downloaded 125 times this past week, and (2) each request has a different DeviceID for the 3DS system from who requested it.

This is how Nintendo is able to ultra ban someone's 2DS/3DS from ever using their online services if they try to do a credit charge back or a person reported theirs was stolen / used by someone else who's not him/her.

Correct. It is. I get this acronym wrong all of the time. Thanks for the correction.

 

It sounds like at the very least you have some issue with the upper screen ribbon cable being damaged or not seated properly, which would cause the issues with the volume slider and tilting the screen. If the cable is damaged you'll need to replace the upper screen entirely.
The blue light shutting off instantly (not fading out as you said) would also be a symptom of that so make doubly sure it's indeed fading out.
The other issues may be firmware or corruption related issues that are fixable with software. TurdPooCharger is the most qualified to deal with that and it looks like he's already on it. Or they might be indications of some deeper hardware problem like the internal flash going bad.

 

Definitely a bad or not properly seated ribbon cable, I can't think of any software issue that would cause that, especially if it's also shutting down when you tilt the screen (there's no tilt sensor in the upper screen)

That doesn't always happen.

It might be multiple separate issues. Like some people said, it might be easiest just to get a new console.