So I was working on a project on my Mac but I kept getting the "33::4" error when I was using rotobrush. I therefore decided to upgrade from Mojave to Big sur so that I could update my After effects since it wasn't compatible before. Now when I try to open my project nothing happens. I doesn't even get a error message, littarly nothing happens and it won't open.
Welcome to the Community and sorry for your issue.
Is it happening with a particular project or any project file? Are you able to open After Effects and create a new project? Also, did you use any third-party plug-ins while creating the project? Let us know, we're here to help.