I am seeing an annoying behavior on my iPad mini 6 when reading a book with the Kindle app: the ‘affordance’ (line) at bottom center of screen does not go away after dismissing reading options (it disappears a few seconds after opening a book, but bring up options makes it re-appear and then it doesn’t go away after that). On iPhone with TouchID it does not have this issue.

Wondering if this happens on the iPad Air 4th generation as well, since like the mini, it lacks a Home button and thus will display the line when the dock is not shown and the app doesn’t make it go away.
Yes this happens on my iPad Air 2020 4th gen. too. As you said it disappears in a few seconds after opening a book, but stays around if I go into options or accidentally display page mode (or whatever they call it). No big deal to me though, although consistency would be better. Some apps hide it, some don’t. Probably an app issue.

ETA: Ditto for my iPhone 13 Pro Max but with a twist. When the affordance line won’t disappear but I switch from portrait to landscape or vice versa then it does. I guess switching orientation resets it on the iPhone 13 Pro Max. Switching orientation on the iPad Air 2020 has no effect though.
Turns out that if you have Continuous Scrolling on (which typically I do on iPhone), then it disappears as I would expect. I also have Orientation Lock Layout setting on, so if I turn CS off I would not have the orientation-change workaround available.

On iPad, there’s no in-app Orientation Lock Layout setting, and unlike iPhone, orientation-change does not hide the affordance once it decides to stick.

It is particularly noticeable for me because I use white-text-on-black and the affordance bar is thick and is the brightest thing on the screen, so it is distracting. Probably I’ll just start using CS more.

I did submit ‘feedback’ to Amazon (for the second time now).

Apple Books handles it perfectly, as does Google Play Books, Kobo Books, and even Nook.
It looks like the latest update (6.56) has finally fixed the persistent affordance issue (which actually affected both Scrolling and non-Scrolling modes, depending on how these were applied).

Wouldn’t you know, the first book I checked this with does not support Scrolling mode, even though it is supposed to support Enhanced typography and Page Flip (according to store listing). Page Flip does not work, and Alignment is not available, ergo it does not support ET. I suppose I will manage to live, even so.
In my experience there are two main reasons why a book that shows Enhanced Typesetting available in the listing does not support it when downloaded.

The first is that the book uses a KFX feature that is not supported by the software version on the reading app or device. That is unlikely for the latest version of the iOS app.

The second is that the book was purchased before KFX support was added to it. That can happen because when a book is purchased you are locked to the version that was current at that time. Any future updates made to it by the publisher are only rarely not made available to prior customers.

If you care to share the ASIN of the book and when you purchased it I may be able to find out more about which situation applies in your case.
https://www.amazon.com/Grace-Kings-Dandelion-Dynasty-Book-ebook/dp/B00KU4O1CY/ref=sr_1_1?crid=2953UESLAFANV&keywords=Grace+of+ki ngs&qid=1650416712&sprefix=grace+of+king%2Caps%2C3 29&sr=8-1

B00KU4O1CY

I bought it 1Aug2015. It doesn’t matter which reading app I use: no KFX features.

And many books I purchased before the advent of KFX now have KFX features, including my first purchase in 2009. But for some reason, this one does not (and in Content & Devices it does not show ‘update available’).

Quite possibly I have other books in this condition, but this is the only case I’ve encountered thus far.

I do have a few non-KFX, non-fixed layout books, but for these the store listing shows Enhanced Typesetting ‘not supported’.
You definitely have an old version of the book.

I was able to borrow that book from my public library to read on Kindle. It downloads to Kindle for iOS version 6.56 in KFX format and supports all of the expected Enhanced Typesetting features including page flip and continuous scrolling.

I examined the metadata of that book in KF8 format to find out when it was last updated on Amazon by the publisher. It was very recently, on March 29, 2022.

Many books were capable of being upgraded to KFX format automatically by Amazon without any need for changes by the publisher. But some were originally published using HTML markup that is incompatible with KFX and require an update from the publisher in order to support Enhanced Typesetting. This is one of those books.

As I stated previously, the vast majority of updates from publishers are not made available to previous customers. Even if you delete the book and re-purchase it you will still get the same version.

You can contact Amazon customer service and politely tell them that you know the book has been updated since you purchased it and ask them to "push" the latest version to your account. They will usually accommodate you in my experience.

That is very likely to be the case if you have been buying books for a while on Amazon.
Thanks. I’ll probably contact ACS at some point to get it updated.

It’s not going to be very easy to discover which other books might have this issue. I have a script that gets me a list of my books (and ASINs), with that I could have a script get the properties from amazon.com, but that won’t tell me which of my books have the issue. Hope it is a rare occurrence.
Sheesh. The not-disappearing-home-affordance bug is back (on iOS devices without Home buttons). I think 6.59 broke it again.

It's not as if they are 'moving fast and breaking things': it's been 9 months since they delivered any new features.
Just got the latest update, with the 'helpful' delete-your-amazon-account feature (6.32).

And the Dock Affordance Bug is back, with a vengeance. It never goes away, not even in Scrolling mode!! What are those developers and testers smoking?

Fortunately nothing has changed with iPhone. The affordance 'sticks' as before if you bring up options during a reading session, but disappears in Scrolling mode.

And with iPads and iPhones with Home buttons, it is not an issue.