I finally made CA work on Linux (using TeknoHamster’s script https://gist.github.com/TeknoHamster/d8b2f90a1cd618074aa1e35c81e7bc4b). Everything works fine, except for these strange triangles.
I have the same problem when running CA on Windows in a VirtualBox machine in the same host system.
My host system is the latest Linux Mint Cinnamon with Proton Experimental.