Here is what I find always occurs in my project with many audio tracks and plugins, and some VST instruments…
Using Cubase 10.5.12 on Windows 10.
Export audio to a new file in, not “Real time”… Cubase interface freezes, and is no longer responsive, even though it renders the file. Cubase process must be killed in Task Manager.
Export audio to an existing file, not “Real time”… Cubase prompts to overwrite the file, which I do, and Cubase continues normally and does not crash. However, clicking anywhere on the Cubase interface, including the “Cancel” button, while the render is in process causes the interface to freeze until the render is done.
Export audio “Real time”… It has been a while since I have done this one, but as I recall the process cannot be cancelled.
This is the dialog as I am exporting for the non “Real time” exports…