My iPhone 12 will not turn on, will not enter recovery mode, and is unable to be detected by my Mac. What do I do?

This iPhone suddenly stopped working a few months ago. I was very busy at the time and after spending a night at T-Mobile and being told they've never seen the issue I had before, I went back to an old iPhone and left it to rest. Now that I have time to spare I want to figure out what this issue is, but I'm at a loss.