If iGlasses only shows black on macOS 10.15 or above, you should check to make sure camera permissions were properly granted.
To check and fix these permissions at any time:
- Open the Security & Privacy section of the System Preferences app.
- Pick the Privacy tab.
- Look for the the Camera section in the left-hand sidebar.
- Click the orange padlock in the bottom-left to make changes, and enter your Mac's admin password when prompted.
- Check the checkbox for iGlasses if it's not already checked. It may be there twice. Check both.
- If it was already checked, uncheck it and re-check.
Then, close all video apps and try again.