for Performance Max can be replicated by pulling from the "asset_group_asset" resource. The specific "performance" field from that report is " asset_group_asset.performance_label " My GAQL query pulls a few other interesting fields and looks like this:
customer.id,
customer.descriptive_name,
campaign.name,
asset_group_asset.field_type,
asset.name,
asset_group.name,
asset.call_to_action_asset.call_to_action,
asset.type,
asset.text_asset.text,
asset.image_asset.full_size.url,
asset.youtube_video_asset.youtube_video_id,
asset_group_asset.performance_label
FROM asset_group_asset
WHERE campaign.advertising_channel_type = 'PERFORMANCE_MAX'