As some already noticed the name Ad Manager is posted regularly in the comments at the Adsense topics.
From Wikipedia:
Google Ad Manager is an online advertisement service brand introduced by Google in June 27, 2018. It consists of two former services, including DoubleClick for Publishers (formerly known as DART for Publishers) and DoubleClick Ad Exchange. It can be used as an ad server but it also provides a variety of features for managing the sales process of online ads using a publisher's dedicated sales team. Should a publisher not sell out all their available ad inventory, it can choose to run either other ad networks or AdSense ads as remnant inventory in Google Ad Manager.
Hopefully we can help each other for those who are new to Ad Manager or who have a problem and want help or for sharing tips and tricks.