That render issue first appeared on macOS Mojave, due to Apple's changes to their version of OpenGL/Freeglut. That got solved with Mojave .3
Then Catalina came along, and I kept on upgrading it with every beta release. All looked good and was working fine for me.
It still is. I'm on the official version now.
The great problem here is: people who've upgraded straight to the stable version of Catalina are getting the issue. I can't seem to identify what's causing it for now.
A few people have sent me their QB64 binaries to test on my machine and, to my surprise, they worked normally, without the render issue.
It is a mystery.
What display do you have? Is it retina? The issue has to do with HiDPI.