How to find Game Update information (Change History) for Games showing on the Manage Games...

Sadly you can't and I think that's a real shame. I would like to see this feature myself.

No, unfortunately, the Xbox doesn’t have this feature. The fastest way I to find out what the updates include would be to visit the Developer’s Twitter or webpage. I’ve noticed a bunch of games and developers are very active on Twitter in regards to updates
and support.

My suggestion is to try in the official clubs for games. Some developers will post patch notes or make a general post about an update being available.

For example, here is a screenshot I took from the official Forza 7 club when they posted about the December update.

https://i.imgur.com/JV1kHxY.png

Unfortunately the only other option, at the moment, is to search online (or they are shown somewhere in the actual game).

Thank you for the timely reply. But what I am actually asking is the details of the update itself, like the change history, the list of bugs fixes and new or changed features, or like information. The size of the update would be nice to know though because
some of them are quite large.

Sadly this info isn't on the Xbox (I'm sure it will come in the future), you will need to go to the developer of the game to see what changes are made in the update.