Changes made from 8.10 to 8.20

Which complete list are you talking about? I'm only getting this:

When the 8.20 update showed up on Express, the feature list was very extensive.  It seemed to include the feature list for many firmware versions not just 8.20.  The list pinned here seems to be the accurate list.

Would be nice if Garmin would include a list of everything they broke for the update.

they write textually from 8.10 to 8.20

Perhaps somebody did not do yet the update, and can do a copy/paste here

And everything they did brake with the update!

those reactions are of course very interesting but not really what I ask :)

What you saw was probably something like this

https://www8.garmin.com/support/download_details.jsp?id=14955

which is for the 8.13 Beta, the 8.20 Production version only had one additional item

• Fixed issue with viewing incidents on the map

which no-one seems to know what it is?

No, I'm about sure it was only changes to 8.20 , but indeed it was a very long list

kingxlight because your 830 wasnt synced in Express since long time and latest "known" version was 7.xx by the app (even if the Edge was on 8.10, there is no firmware version sync via cloud between GC and G Express) and in this case the Express shows the full changelog from the latest known 7.xx till 8.20. But the real changes were only those few lines. I hope it is clear know. 

I have done even each beta update ...
Let us close this post, it is not that important