Since Apple released the first Beta of iOS 16 after the presentation at WWDC 2022, many weeks and six Betas have passed, and it seems that the engineers in charge already have the definitive version for iPhone ready, not so for iPad.
Mark Gurman has said so in his latest newsletter (link): Apple engineers have completed work on the final version of iOS 16, which will be released in the coming weeks. This does not mean that there will not be new Betas before the launch of the public version, far from it, since the normal thing is that the Betas that see the light have already been prepared for a week or two, so we could still see one or even two betas before the public version, which is usually the same as the last Beta released. The iPhone 14 presentation event takes place on September 7, or at least the latest rumors point to it, and the sale begins on September 16. Everything seems to fit.
What we will take longer to see is iPadOS 16 and macOS Ventura. As has been said in recent weeks, the updates for iPad and Mac will take a little longer, a delay that is mainly due to problems with Stage Manager. The new multi-window that Apple announced at its June event still leaves a lot to be desired in terms of functionality, and will need further refinement before the final version is released to the public. Gurman points to the month of October as a possible release date, maybe coinciding with some new iPad and Mac presentation event, and maybe creating a new pattern of releases that will continue in the future. The intimate relationship that iPadOS and macOS are acquiring makes an independent launch of iOS and watchOS make a lot of sense, systems that also go hand in hand.