Google said the other day when it was retiring:
We’re removing ad balance from AdSense accounts on May 20, 2020. We’ll also remove the ad balance experiment option, including all completed ad balance experiments, on this date. If you’re currently using ad balance or running ad balance experiments, we’ll email you with additional information. If you’re not using these features, then you don’t need to take any action. We appreciate your patience and understanding as we continue to develop our products.