Teensy 4.1 fuse location

The "fuse" is a self resetting type. It doesn't "blow" like an ordinary fuse. It's really just a resistor that greatly increases resistance when it gets hot from too much current flow. It returns back to normal when it cools down.
well that's not the problem, something is shorted and pulling the 5v down to about 2.5v and there is no 3.3v. I'm just going to order a new replacement.
If "no 3.3V" means zero volts on only a few mV, usually that means a metal short has happened. Often those problems are recoverable if you can find the stray metal and remove it.

But if 3.3V measures some small voltage like 0.6V to 1.0V, usually that means a semiconductor short somewhere inside the chips. That sort of failure isn't usually fixable.