Same issue here, it looks like it takes a very long time.
I found out that you can get a current status via the „Console“ App, just search for „brain“ and you‘ll see semi regular updates about the progress from softwareupdated (every few minutes)
Currently the progress is at 30% after 20 minutes! It seems there‘s a bunch of hardware updates happening with signing of configurations in between - needs to have a stable internet connection!
Thoro
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