Sorry, but that's neither the issue nor the problem.
Installing Compiz is easy (compared with configuring it), but even following @Wimpy's install instructions many, many MATE-specific files are NOT installed. Eg. on 18.04 Compiz CCSM > Preferences > Profile is set to "mate". That's not possible under 20.04. At least 1 file related to this is /etc/compizconfig/mate.ini, a 191 line file covering ~30 attributes. But that file's not available - along with many others - in 20.04 after installing compiz-mate. That's the issue that I'm trying to report ...
And without window decoration, window controls and the ability to move windows it is very difficult/tedious to debug on a small laptop screen!