gtk3-mushrooms certainly works nice for GTK apps I use on my main Manjaro (KDE) desktop.
I was experimenting and kind of compiled it on Ubuntu MATE 19.10, but it doesn't look like all the patches were working -- likely I haven't compiled or installed it properly.
The experiment lies here if anyone wants to try and get it compiled/installed properly on Ubuntu MATE:
It's recently had a different maintainer, whom doesn't appear active at the moment. I created an issue suggesting the tab scrolling with mouse wheel patch (#25). Personally, I like this idea to install an alternate GTK3 package providing the desired "classic" functionality, even if it means carrying a warning label. 