Are you interested in having the lovely new Yaru-MATE theme but are running Ubuntu MATE 20.04?
We have some good news ! Wimpy has just created a PPA which backports those brand new themes into our latest LTS release.
To get this new goodness, add the following PPA and update your system.
sudo add-apt-repository ppa:flexiondotorg/yaru-mate
sudo apt-get update
sudo apt-get upgrade
A very nice and detailed write-up about this: