Dorico froze

Dorico froze yesterday: intractable “Application Not Responding”. After considerable time, I Force Quit, but there doesn’t seem to be any appropriate log messages.
I was switching between two small documents, and it was spinning beachball between each one quite a lot.

You will see the beachball when switching between open projects because Dorico is unloading one set of sounds and then loading the sounds for the newly-active project. In due course we will change this such that Dorico won’t automatically activate the project you switch to for playback, so you’ll have to explicitly activate the project you want to play back. (This is how Cubase handles multiple open projects, for example.)

Is it possible to switch off the whole VST sound thing?

Not really at the moment, no. You could try moving the whole of the bundle out of Contents/Applications inside the bundle (right-click and choose Show Package Contents). Obviously you’ll get no sound of any kind, and nor will input from a MIDI keyboard work. And this is not really a supported way of using the application.

I had the same problem today. I could not even do anything with two documents open. I found a solution:

On the Play mode section, I changed the VST Instruments dropdown from Halion SE to —, and I did this with my first document before opening the other one. Then I did the same change to the second document. After that, no more problems.

This is of course not switching off the whole VST thing, but you could always try and see if this works for you.