If you are using a device with macOS 10.15 Catalina or newer - you must grant additional access to the Screen Recording for browser.
1. Choose Apple menu > System Preferences, click Security & Privacy, then click Privacy.
2. Choose «Screen Recording».
3. Select the checkbox next to an app to allow it to access your Screen Recording.
If you see these settings, but can't change it - unlock Security & Privacy preferences. Click the lock icon to unlock it, then enter an administrator name and password.
If the "Provide access to the screen" window appears, but immediately disappears, thus not allowing you to click the Share button, right-click on the Google Chrome icon in the toolbar (at the bottom of the screen). You will see a list of all open Windows. Find the "Provide access to the screen" window among them and use it.