Amusing side fact. That demo.gif is 7 times bigger than the application binary.
Made a video on how to use Chrome DevTools in applying this technique: https://www.youtube.com/watch?v=yRrrL0Mg1pM
One problem - I'm unable to resize the window and make it smaller.
But after doing a clean install of macOS 10.15.3, everything’s been fine.
I expect 10.15.4, currently in beta, to be as stable as any other version of macOS at this point in its lifecycle.
Turns out that Sidecar doesn't work if your mac is connected to a VPN, even if you are connected to your iPad via USB with its wireless turned off.
I would say having a delay of 3 months give or take is usually the best practice.