I use Ubuntu every day, so I can notice the difference, never had this problem before. When I just type in RubyMine, I have to wait until the chars become visible, up to 1 second. When I collapse/expand folders, I have to wait. But when typing in terminal, in Chrome, LibreOffice no problem. You may say it is a RubyMine problem, but it worked fine on 17.0 and before, it works fine on macOS and Windows also. I have an iMac 2017, 32 GB Ram, macOS 10.15.7, only one VM running. No hard background jobs, CPU load close to 3%. VM has 2 CPUs, 8 Gb RAM, 64 Mb graphics, 3d acceleration, more space. The Ubuntu installation is fresh, because previous Ubuntu VM did not load after upgrade, it boots and hangs forever on black screen. I had to create a new VM and migrate data from old HD. Congratulations on improving the login screen, I was waiting for that so long, but you introduced another problem.