Sigh, I have the worst luck with soldering. As I mentioned, I soldered the first board, trying to solder in stacking headers by having some space between the header and the board. It didn't go so well, so I cut off the stacking header, and unsolder the pins. But I lift the plating from the top part of several pins. So I convert the board into a normal Teensy, soldering the header on the bottom, but I won't be able to put castlelatted boards on that.
I got out a second board, and soldered it up just using normal pins, and it seemed to work. However, I had several pins on the right side that were not properly soldered in (3.3v, pins 22-18, and pin 16). So I attempted to redo the solder connections. But now I presumably have a solder bridge somewhere, and the Teensy 4 is getting hot to the touch and quitting after a few minutes. Tomorrow, I will attempt to unsolder all of the connections, and redo them. But I suspect the issue was I probably damaged the board having the solder gun at max as I was removing some globs of solder and I probably kept the iron on the board too long, and reflowed some solder on the PCB itself and made a short.