how do I undo Shift-Command-5??

If you have a MacBook Pro with touchpad look for a red dot, press it.

Otherwise try restarting.

https://support.apple.com/guide/mac-help/take-a-screenshot-or-screen-recording-mh26782/mac

Click the "Options" button for other other choices.

isaarguello wrote:

how do I undo Shift-Command-5??

my screen is permanently with a lighter square where the screenshot was placed and the rest is a lot darker and it does not change

You can see all your options:

Take a screenshot on your Mac

Shift, Command, and 5. You will see onscreen controls for recording the

entire screen, recording a selected portion of the screen, or capturing a still image of your screen:

How to record the screen on your Mac - Apple Support