Glad to hear that it's at least booting reliably for you now. Thanks for testing that. I'm sure you have done this already, but you should also check with the plugin manufacturers for Big Sur news/updates.

Regarding the audio edit window, in my testing on Big Sur 11.1 beta, drag and drop to the Audio Edit window appears to be working, although I notice that it is a little "finicky" - e.g. if I start dragging and wait too long before releasing the mouse button, then it doesn't work. If I drag and drop quickly it does work. Also I do not have any issue with the size and/or placement of the confirmation dialog...
PG Music Inc.