I've seen that AppleVis has made a fairly favorable review of new accessibility features in iOS 16.
However at the same time AppleVis has retweeted the tweet of the developer of one well-known app who claims that text-to-speech in iOS 16 is unusable (literary that word). He further explains that this comes from highlighting issues.
Those two things appear to be quite in conflict so I'll try to explain this from the technical side as I am also a developer of one such app.
First, I must agree that the highlighter problem does exists in iOS 16. I must also stress that highlighter has never worked perfectly in iOS so it isn't something completely new, just those issues are now more likely to appear and to be more severe.
However I really cannot agree that this makes text-to-speech in iOS 16 useless. In well made apps this shouldn't go beyond making slight and barely noticeable visual issues. Those are completely irrelevant for VoiceOver users. I do agree that if the app is conceptualized in some specific way that is on the opposite side of good practice this can accumulate and lead to unbearable experience. However you cannot say that text-to-speech on iOS 16 is unusable for the simple reason that your app concept is not compatible with it and likely not made with some good developer practices as I can't see other apparent reason why that could happen.
Is it worth to upgrade to iOS 16 as of today? In my opinion the general answer is yes, especially if you use VoiceOver. There is too much to gain and too little to lose. Eloquence voices are great for speed reading. New Premium voices (especially English UK variants) are as natural as the voice can be - much better than any other offline voice and only comparable to something that was offered through online services in apps like Speechify for 140$/year.
I do understand that some people have invested a lot in that app and don't want to invest again, but if you are a VoiceOver user (and most people here are) you can use my app Speech Central completely free, so it is no sales pitch just my donation to community. And it is in no way a 2nd grade app, actually overall it is more capable than any other app, I have made a fact sheet that covers over 100 features to prove that: https://speechcentral.net/speech-central-vs-voice-dream-reader-vs-speechify/