Performance Max removed most of the manual controls advertisers relied on. What remains is the feed, and it turns out the feed was always doing more of the work than the bidding.
Title structure is the single largest lever. A title built as brand plus product type plus key attribute plus variant, ordered by how buyers actually search, routinely outperforms the manufacturer default by a wide margin.
Beyond titles: complete GTIN and attribute data, custom labels that let you segment by margin and inventory position, and supplemental feeds to fix data you cannot change at source. Feed work is unglamorous and it beats bid tinkering almost every time.