You can deploy an Ubuntu 20.04 cluster with Easy8. Just select Ubuntu 20.04 when you download the ISO. If you have an existing 18.04 cluster, you will likely run into problems if you try to do a distribution upgrade. This is because you would have to switch the repository path for the Bright packages to Ubuntu 20.04 as well. It might work if you do this, but likely nobody has ever tried it before so you will almost certainly run into problems one way or the other.
It is strongly recommended not to do a major version upgrade of your Linux distribution.