jianteng113 wrote:
My Macbook is just updated from 10.x version to 11.3.1, but the application of "Grab" doesn't work. The icon shows as "question mask". How should I do to restore the "Grab" App? Thanks.
You do not, the app is no longer supported it has been replaced, with ScreenShot.app in your Utilities folder.
Shift Command 5 —see options

How to record the screen on your Mac
https://support.apple.com/en-us/HT208721
Take a screenshot on your Mac
https://support.apple.com/en-us/HT201361
The key shortcut I do not see mentioned is Shift Command 6 for capturing the current Touchbar, typically used when trouble shooting and clarification when interacting with Support.