I know that anything more than 5v touches any GPIO then it’s dead but I was changing the wiring and accidentally plugged a 12v 2A (for motor supply) connector to a female connector which leads to GPIO pins 20 and 21 for a very short amount of time, maybe a second; ofcourse the PI tripped and got reset immediately.
Now, I didn’t let it power on for a minute and powered it on again. It crashed several times till the splashscreen showing it’s logo and then booted to the desktop finally after few crashes.
I immediately noticed the cpu load percentage on top right being constantly above 25%(unusual) and the power(lightning) logo in the top right stayed there constantly as well so I touched the pi and it was too hot to touch so I immediately switched it off and haven’t turned it on since.
I looked up the internet and there’s mention of a fuse which resets over time but observing the behaviour, my question is, if it boot up to desktop, is it fine and will it reset?
A second is not a short period of time for a computer which executes millions of instructions per second.
Neither is it a short period of time to damage hardware designed to handle no more than 3V3.
You have probably destroyed the directly connected GPIO. The damage will likely spread throughout the SoC over time.
Time to buy a new Pi.
The polyfuse isn’t really there to protect the Pi (and would not have helped in this case anyhow as you bypassed the polyfuse). The polyfuse is there to prevent a current large enough to start a fire flowing through the Pi.