[Quoth]

Forget final formatting. There are zero decent programs for that on iOS or Android.
You need a laptop with Linux, Mac OS or Windows, with either LO Writer, or maybe older versions of MS Word.
If you are not swapping the SAME document with a Word User every other day, then LO Writer from LibreOffice 6.x series is the best solution now. Learn how paragraph styles work and levels work.
You only need page styles for paper output via built in PDF.

You need Calibre or Sigil to make ebooks, basically epub2 as that is the upload format for Amazon also. Recently using odt to Calibre seems to work as well as Save As (additionally) in docx and convert in Calibre.

Jota is fine for basic editing on Android eink. Absolutely forget formatting. You need a 1600 x 1200 or 1920 x 1080 screen minimum, much more CPU and RAM than most ereaders or tablets and no full featured wordprocessor works well on eink.

There aren't even any commercial or Web based options that will do what you want, even on a 10" eink tablet, never mind more affordable 7" and 8".

I had even a Win10 tablet with MS Office and it was rubbish compared to a real laptop from 2002 (1600 x 1200 P4 mobile) or from 2016 (1920 x 1080 non-glare screen, i5 with AMD GPU, 500G HDD, 8 G RAM and about €600!).

You'd buy a Likebook Mars (7.8" eink Android, SD card), a 10" Lenovo Tablet, A 7" Kobo Libra, a decent BT keyboard and a moderately good laptop for the price of a decent 10" eink and decent keyboard.