I'm not an expert, but since no-one else is replying I will share my experience.
Firstly, I assume you are looking for chapter information, as in the attached screenshot.
If so, then m4b files are not the only file format that supports this, and in fact I have seen one of two mp3 which did have embedded chapter information, but this is unusual.
There are some apps/players that can work out the chapter information from multiple mp3 files based on the file name. BookPlayer tries to do this, but they still recommend using M4B. See
https://github.com/TortugaPower/BookPlayer/wiki/FAQ for more details.
That page also recommends a few programs that can convert mp3 to m4b files.
For example, on windows I have used AudioBookConverter to convert multiple mp3 files to a m4b which I have transferred to my Ipad and play using apple's Book app.
There are a few issues this program. It looks like if you change any of the settings, you need to exit the program and reload before they take affect. Also the current version has an annoying bug which asks if you want to download a new version, despite there being no newer version. But it works once I had it configured, all I need to do is add the files and start the conversion process and it can work out the chapter details itself.
There are also advanced features in this program that I don't use, but it is possible to amend the chapter details, e.g. to add the name of a chapter.