I started this thread six weeks ago and haven't found a satisfactory answer, but one dodge I can offer you that works - BUT ISN'T THE ANSWER - switch the audio source from DAB to phone media by briefly starting and stopping a podcast, audio book, spotify or whatever. Then you audio is phone audio and not the Radio, you'll have Voice Guidance BUT no radio.
In one of the tiles on the screen I've always got one of the above so for me it's not impossible but not how it should be.
One of my first tries, but not this.
Not tried this but another dodge that isn't ideal, I'll explore though
I think TGG's issue and certainly mine is not having Voice Guidance play over 'any' radio but it doesn't mute the DAB radio and play voice guidance over that. This is an issue because, for our 4 anyway, DAB is the car wake up audio source even if last use was AA, next day you jump in and drive away and it's back to DAB and then won't mute for VG