Here are 3 setups using one other piece of software for web browser to QLab Camera Cues that work in Catalina.
(Other methods are available some of which use chains of programs e.g NDIScan Convertor to NDI Syphon)

1 CamTwist

Desktop+ source confined to specific Chrome window. You may get occasional black flashes with this.
2. OBS Virtual Camera
Possibly a bit more processor intensive, but bringing OBS output into QLab and vice versa opens up all sorts of possibilities. Uses a window source on OBS . Virtual Camera must be started in OBS with button on bottom right of window (Currently showing Stop Virtual Camera)
3. ChromeSyphon
More recent than CefWithSyphon, which it is based on, but still over 4 years old. It is a standalone, very simple browser with Syphon output built in. It runs an outdated version of Chrome so there may be security implications.
Mic