In order to Share content from a Mac for applications such as MS Teams, or the T1V App, Screen Sharing will need to be turned on.
You will be prompted to grant permission the first time you try to share your screen. Select Open System Preferences from the prompt.
If you miss the prompt, you can do this anytime by going to Apple Menu > System Preferences > Security & Privacy.
Under Screen Recording, make sure Microsoft Teams is selected.
Go back to your meeting and try sharing your screen again.