Today I learned that not all pins on the 40 pin header are "gpio" pins
I was trying to figure out if I could power the raspberry pi 4 via the "gpio" pins and was reading some conflicting information. It wasn't until someone in a forum said "you can't use gpio/signal pins to power the pi" but also added that the 5v "power pin" on the 40 pin header would work. I will never think that all header pins are gpio pins again. Cheers.
I've powered a Pi with the 5-volt pin, but you have to be sure you're using a good regulated power supply.