In order to share your screen on a MacBook, please follow these steps:
Click on the apple icon:
Select System Preferences tab:
Once there, please select Sharing icon:
Tick the box Screen Sharing
Note: if you have ticked Remote Management, you will not be able to tick Screen Sharing, so if this is your case, please untick Remote Management.
And that’s it from Macbook side, now you only need to share your entire screen on Google meeting by following these steps:
Click on the Share Screen icon and select 'Your entire screen' option
Make sure to click on the screen so the 'Share' button will be enabled.