So you're seeing green rectangles everywhere, oh no! You may be hearing a narrator, and none of the UI is working properly. Congratulations, you have turned on Android TalkBack. More generally, this is known as speech over or voice over. It's like hitting the Shift key too long in Windows, with similarly annoying results.
This is unfortunately very easy to do, because there is a stupid, secret gesture for this. As of this writing, the gesture is pressing and holding both the volume up and volume down buttons. But in the future, it could be anything. Whatever the gesture is, try doing it again. If you're lucky, you'll stumble upon the right combination and manage to turn the feature back off.
Rebooting has broken. Rebooting does not fix the problem. There was never a prompt to persist the questionable setting across reboots, but alas here we are anyway.
Swiping and scrolling have broken. You cannot swipe or scroll normally to leave the current application. Nor to activate the main settings drawer to disable TalkBack. You may be stuck on the camera app, taking hundreds of photos of nothing. Or stuck on the soft reboot panel, trying very hard not to accidentally commit a felony by dialing emergency services. TalkBack screws up swiping completely. You may be able to swipe and scroll by using two fingers instead of one. Requiring more fingers to complete a normal gesture is the opposite of "accessibility" but such is the state of softare in the 2020's.
You can't even adjust the voice over volume with one finger. Mine happened to be stuck at 0%.
In Google's brilliance, they never implemented a way to navigate from assorted settings views to the main settings view, which would have made it easier (more accessible) to get to the TalkBack options and turn them off.
As soon as you are able to temporarily disable TalkBack, remember to visit the main settings application and disable the TalkBack gesture.
You cannot select the app or settings drawers. You cannot select the scroll bar. You cannot select and scroll. You cannot do much at all. This is because tapping has broken. If you try to select the bottom left or right buttons on the lock screen, you may be told to press and hold them. Pressing and holding them does nothing. Pressing on help hyperlinks in TalkBack dialogs does nothing. You can select things by pressing once, and then in a second phase of the NASA approved tap procedure, activate the thing by double tapping.
Bonus tip: Try swiping/scrolling normally with one finger. Swipe up to increase the talking speed, so that the UI can operate at a snail's pace rather than paint drying pace.
If you're reading this, you very likely found it by another device. Because without knowing these tips, you probably can't reliably navigate to a Web browser on your primary Android device in order to lookup how to turn off the green rectangles. Your fingers are moving too quickly, and you end up stuck in some random ass app. Spread the good word so that someone nearby can assist you.