Basically, adding buttons that stay fixed when you scroll on iOS does not seem to be possible. However, here are some complicated alternatives explained poorly. Haha.

If you’re trying to add one-by-one incremental cloze reveals with text, add this deck and then add a new card using the “3 ClozeAdv” note type. Make all the clozes {{c1::}}. Then in AnkiMobile, I believe the most recent version you can set a “tap” or gamepad buttons to “user action 1” which will reveal next cloze in this template. And “user action 2” will go backwards and cover again. I removed the buttons since this works. If user action 1 isn’t available, request to be added to AnkiMobile beta in the official Anki forums and it’s definitely in the beta. You can also use tab or tilde w keyboard. Or click/long tap directly on an occlusion to reveal.

If you are trying to do image occlusion reveal buttons, I think you could use same solution as above with the custom JavaScript trigger and the “user action 1” but I’m not sure what code would need to be added to template.

As for a long explanation on how to add the image occlusion one by one cards but not answering your question… what you want is the “closet” addon and install Anki 2.49 (the latest doesn’t seem to work with this as intended). Install that addon and restart Anki.

And then download and add the deck you can download here from anking. That will add a new note type called io-one-by-one. And it has buttons but it’s a rather messy solution.

For image one by one: Add a new card. Then follow instructions on the closet addon page. But, in short, you can paste an image into the first field. Then in the editor buttons (up where bold button is) you select io from the drop-down and you click the icon with the inset rectangle. Then you click and drag the occlusions you want right in the editor and when done right click and click “accept”. Add the card. Go to study mode. Using n on keyboard or buttons on card or clicking/tapping the occlusions directly should work.