Since you're specifically trying to write—a book, I guess—it may be worthwhile trying to find an app designed for that. A quick search came up with Draft (https://draftin.com/) and Reeday Book Editor (https://reedsy.com/write-a-book). I haven't used these myself, so take a look around. Source: over 1 year ago

Similarly, cloud based Markdown editors such as HedgeDoc, StackEdit, HackMD and Draft among others are not great choices for those who don't have Markdown experience, plus are a bit more barebones than desired for project management. The same applies for LaTex collaboration software like Overleaf. - Source: dev.to / over 2 years ago

I'm willing to work on a royalty share deal or a fixed fee (PFH), so I'm offering you an opportunity to submit me your work. The story that I connect with I'll do the graphic part for, finalize the audio and pay for the https://publishdrive.com/ fee so we can make some income together, even a little ;). Source: about 1 year ago

Draft2Digital. https://www.draft2digital.com. It’s for E-books. They are testing a print service and I’m still on the waiting list. Publishdrive https://publishdrive.com. Never used, but they they charge a subscription instead of taking part of your royalties. Source: over 2 years ago

PUBLISHDRIVE: Publishdrive requires a monthly payment to publish your books. You get more royalty, but it will cost more each month. There is an App sumo coupon running around if you want to try it. I would be very cautious and read the fine print. I don’t use them. They are kind of a nightmare to deal with. Source: over 2 years ago