Multicam broken in late PP late 2019 and 2020
Since the September release of CC2019 and CC2020 Multicam is just plain broken on a PC (don't know about Mac - haven't tested.) Here's a screen grab from CC2018 (which works as expected) .
Note the background has disappeared and we have a typical 4-way multicam split. Everything works. Clicking on a box while playing cuts to that camera. When not playing it changes the whole clip. When not playing and control clicking it inserts a cut. Now lets take a look at the exact same media and setup in CC2020 (same problem in late CC2019 but we'll stick with 2020 as the problem has not been solved.)

The first thing you'll notice is the background palette did not reset to grey when going into multicam mode. Mouse clicks no longer work in static mode at all (well they sort of do the very first time you enter multicam but the clicks seem inaccurate - sometimes you have to click slightly above your intended target or it just doesn't work at all) then they stop working after you play once. When you first play the multicam it actually cuts ok. But the first time you stop it, it stops working and only going in and out of multicam gets it working again. I've updated video drivers etc to try and get it working. I've had the two apps (CC2018 and CC2020) open side by side to try and work out if any settings have changed. Everything is as identical as it can be. Including project settings like CUDA playback, Mercury transmit etc. Works in CC2018, doesn't work in CC2019 on the exact same computer with the same settings.
Anyone with a solution I welcome it.