The changes history is in beta testing.
You can view all changes that you make to your ad campaign settings on the Changes history page. From there, you can go to your campaign page. Your history saves data about any actions you take that affect your impressions, such as when you:
Launch or stop campaigns
Make changes to campaign parameters (for example, to the schedule and geography of impressions, strategy, bid corrections, or network settings)
Launch or stop impressions for individual ads
Transfer ads or campaigns to an archive or get from an archive.
The changes history does not include entries for when campaigns launch or stop automatically because your daily budget limit was reached or because there is not enough money on your account.
The changes history has been available since April 9, 2018.