If you have a Macbook Pro with the butterfly keyboard (2016 - 2019 models) and one of the keys is stuck, try this fix:
Pick up your laptop and turn it upside down. Note the position of the stuck key. Using two fingers, simply give the bottom of the laptop a bunch of firm taps in the area of the problematic key.
Right the laptop and set it down. Push the problematic key repeatedly. It should pop back into place, if it didn’t during the inverted step.
This morning the “U” key on my Macbook Pro became stuck in the down position. I read three pointless articles and watched four videos until I finally found the trick I just described. I hope someone Googles for how to fix it and finds this faster than it took me.
https://www.core77.com/posts/100566/How-to-Fix-a-Stuck-Key-on-a-Macbook-Pro-Butterfly-Keyboard-2016-2019-Without-Using-Tools-or-Compressed-Air