Selected a new text annotation box, right-clicked it, selected "Edit Text".... BOOM.
Sad to say, you've hit the #1 crash on Camtasia Mac 2018. I am implementing a fix as we speak. It only happens when you are working on a project after you have previously closed a project. So the workaround in the meantime is to close Camtasia when you close a project and then reopen it. You shouldn't have to do that, but for the moment, knowing this may save you some heartache.
And thanks to all for submitting crash dumps. This is how we find the issues that are effecting users and get a chance to fix them. You should be able to edit all you want as long as you don't close any open projects until you are done (or if you do close a project, then close Camtasia and start it up again).