Thanks for the reply. I think you’re onto something there. I know that the latest version of macOS, Catalina, has some beefed up security measures. When I check camera access in the Privacy and Security section of the Preferences, UE4 is not listed there (but Parallels is, which might explain why the camera is accessible from UE under Windows). Unfortunately, there appears to be no way to manually add an app to the permitted list. Usually, when an app attempts to use a privileged device, macOS automatically displays a dialog to grant access. That never happened with UE, so I’ll have to figure out how to grant it permission.
You’ve pointed me in the right direction, so thanks!