Well there is this post: https://intellij-support.jetbrains.com/hc/en-us/community/posts/360007962380-2020-1-update-breaks-font-and-Material-theme-
I do not have a font issue (I use Consolas), I have the issue with the side colors. Where in the old the side was also nice and dark like this:
In the new one it is more lighter:
In other words Material Darker is not being applied on the side tab and other windows.