Monterey (and later), and mac ARM
Is kJams currently compatible with Catalina?
No. You can not run kJams under macOS Catalina.
Why not?
kJams is currently a 32bit application, and Catalina does not support 32bit apps.
When will kJams be able to run under Catalina?
The hope is "some time in 2020", the optimistic hope is "mid-2020".
How can I run kJams today if I have Catalina?
You can't. I thought you could download Mojave from the app store, and use that to install in a virtual machine, but Apple has removed them from the app store??