The latest macOS operating system update does reset your security preferences. You'll have to fix this by following these steps:
  1. Launch “Zoom” on your Mac and start a new meeting.
  2. Once you’re in an active meeting, click on the “Share Screen” option from the bottom menu.
  3. This will open a new window on your screen. Here, you’ll be able to choose your desktop for screen sharing. Click on “Share” to get started. When you’re prompted to give Zoom the necessary permissions to share your screen, click on “Open System Preferences”.
  4. This will automatically take you to the Security & Privacy section. Here, choose “Screen Recording” from the left pane and check the box next to Zoom. NOTE: you may have to click the little padlock icon in the lower left hand corner to make changes. Ultimately, you want Zoom to be checked in this menu. If Zoom is greyed out, click the padlock, you'll be prompted for your machine's password, and then the padlock will "Open" and you can check the box next to Zoom. See photo below. You may be prompted to relaunch your Zoom, but that’s not necessary. You can close this window and go back to Zoom.