Florida added on September 16 (with its own added claims against its state laws).
This article had a concise explainer of the central issue: “The [FTC’s] lawsuit’s central dispute is not whether advertisers could set a maximum bid, but how Amazon determined the amount charged when an ad won.”
And as an Amazon Advertising customer (though not for many years), this is the first I’m hearing of these other factors besides bids that Amazon alleges contribute to final pricing. 
Is that new?
Amazon says advertisers never pay more than their maximum bid. It also says its system uses hard and soft reserve prices and evaluates ad relevance alongside the bid, rather than selecting placements by bid amount alone.