Now here is an app that will place chapter markers into your MP3 file: https://chaptersapp.com/faq/
I am sure there are others. Note that it only works with selected MP3 players.
If your Audacity project has labels to mark sections, perhaps, you can FIle > Export >Export Labels into a text file. Then you could use a spreadsheet to convert the markers into the proper format.
If the labels are to be at regular intervals as you indicated, perhaps your “chapter app” will do that for you.
I initially split the file into 5 minute segments and then exported as multiple tracks.
This works for what I need, but I will explore the app you suggested although I’m unsure if the iPhone / iPod supports it.
I believe that app will support iPhone / iPod although I might, for now, withhold using ii as it costs £20 and I only have one track that I have a need for it just now.