@pascal said:

I wonder if there might be an incompatibility with the Universal Audio audio driver? This has been happening ever since I installed it for a sound card.

Could be. Have you tried removing it?

Just out of curiosity, could you download Isadora 4.1.3 and see if it launches? (Isadora 4 and Isadora 2 can be installed on the same computer without interfering with each other, and you can try launching Isadora 4 in demo mode, without a license, just to see if you have the same problem.)