I have installed, uninstalled (back to 3.31), and reinstalled version 3.4 on my iMac 2017 and 3.4 locks up when it attempts to "prepare a scene" (White background only).
In an attempt to make sort it out I created a new simple project in 3.31 using Dr. Applesmith, installed 3.4, which then attempts to open the last opened project and it worked for a short time but when I then opened a previous other project it locked up again.
It appears all other new Adobe apps (PS, PP, AE, AU) are working.
When it locks up, is the mouse cursor turning into the spinning color wheel cursor, and you can't even click anything in the Scene panel? If clicking in the Scene panel does seem to respond, can you try holding down the Option key as you click the Refresh Scene button in the lower-right corner of the Scene panel. Does that help at all?
If you launch Version 3.4 and then immediately hold down the Option key as the app is launching, does that allow the app to launch with a new project? If so, if you then create a new scene (Scene > New Scene), then open that scene, is it still locking up?
Just checking if it's just any scene (even an empty one) that's causing the issue, or if it's an existing project with content in a scene. If an empty project/scene works, what happens if you then go to the Home screen and select the Chad (Photoshop) puppet? Does that also lock up when preparing the scene?
Sorry, from your earlier reply, it sounds like it's mainly happening with an existing project from Version 3.3.1. If in Version 3.4 you create a new project then import the older project into it (i.e., File > Import, then select the .chproj file for the older project), does that make any difference?