The setting
Microsoft Advertising added an option to exclude Audience Ads placements from inside a Performance Max campaign, reported by Search Engine Roundtable on 6 August. No further detail on rollout scope or timing accompanied it.
Placement control is the long-running argument about Performance Max on both Google and Microsoft, so a switch that removes one inventory type from the blend answers a complaint advertisers have been making for years. It also arrives without a way to answer the question it raises.
What to do about it
Establish a baseline before you exclude anything
Record current cost, conversions, and conversion value for the campaign across a stable period before touching the setting. Performance Max reports the blend rather than the parts, so once Audience Ads are excluded there is no retrospective view of what they were contributing. The only comparison available afterwards is against numbers you captured first.