I was able to replicate that the program will crash when a new project is created followed by pressing the new project button. I have resolved the issue and the program will resume functionality instead of crashing.
I believe I fixed this issue in the very latest update. If you download the program again the issue should be resolved. I updated this page with information on the fix:
https://actiongameraaron.itch.io/squeaker/devlog/479618/version-0311-fixes-a-cou...
Thank you very much for your bug report.