We recently announced  that Top content bid adjustments are no longer available for any campaigns. To align with this change, Google Ads API will make the following changes starting November 1, 2022 .
  Attempting to set an AdGroupBidModifierpreferred_contentContextError.OPERATION_NOT_PERMITTED_FOR_CONTEXT 
  Attempting to retrieve an AdGroupBidModifierpreferred_contentbid_modifier 
 
If you need to retrieve the existing values for these fields for future reference, we recommend that you download these values before November 1, 2022 .- Anash P. Oommen, Google Ads API Team