I updated my app to the new Mac beta and on restart my Mac won't boot and there is no volume to recover. Has anyone else had this issue? (sorry no app version number known because I can't start my computer)
It sounds like after your upgrade to the new Dropbox Beta for Mac, your device won't start whatsoever. If this is the case, then the Dropbox app might not be entirely to blame for that.
Since the device isn't able to start at all, it might be indicating deeper issues, a faulty OS or more. In any case, this is something that you'll need to check with an Apple specialist, in order for them to guide you with the appropriate steps.