The newest Mac OS update, Big Sur, has implemented additional security / privacy features that disable screen sharing in Blackboard Collaborate. In order to re-enable the sharing features of Collaborate, the following steps should be taken.
Select the Apple menu on the top left corner of your screen. This will open a menu. From the menu select System Preferences.
This will open your system preferences. Select Security and Privacy.
This will open your Security & Privacy settings. You may need to authenticate to make changes. Click on the Privacy tab and in the left menu, scroll down to Screen Recording. Check the box next to your Chrome and Firefox browsers in order to allow the browser to share your screen.
You will be prompted to restart your browser.