The changelog is in beta testing.
You can view all changes that you have made to your ad campaign settings on the Changelog page. You can get to it from the campaign page. Your history saves information about any actions that affect your impressions, such as when you:
Start and stop campaigns
Make changes to campaign parameters (such as the display schedule and region, strategy, bid adjustments, or ad network settings)
Start and stop impressions for individual ads
Archive or unarchive ads or campaigns
The changelog does not include entries for when campaigns start or stop automatically because your daily budget limit was reached or because there is not enough money on your account.
You can view changes as far back as April 9, 2018.