If you're using a Mac, you'll need to grant permission to Teams to record your computer's screen before you can share.
1. The first time you try to share your screen, you'll be prompted to grant permission. From the prompt, select Open System Preferences .
If you miss the prompt, go to the Apple Menu, click System Preferences , then click Security & Privacy.
2. Locate Screen Recording on the left navigation. A list of apps will appear that you can allow to record the contents of your screen. Click the checkbox next to Microsoft Teams.

If you are unable to select Teams, you may need to click the lock icon in the bottom left corner of the menu and enter your password.
3. Return to your meeting and try sharing your screen again.
Please note, if you're using Teams on the web, you will need to also grant screen recording permission to your browser.