I have not tried Quoll Writer, but it sounds interesting. When my work life returns to sanity I will probably take a closer look.
Now, the real question is whether you are working on an epub or a book?
You can write your book on anything that works for you. For narrative fiction, at least, choosing what works best for the writing process is much more important than worrying about publication issues (eg: generating an epub). For non-fiction there can be reason to think ahead to publication.
You will find some others here like Scrivener very much, and there is a very good Windows version of that available. It's not free, but it's not expensive and they give you a good trial period and an excellent tutorial.
I use LibreOffice with a (slightly customised) epub plug-in, the result of which I then clean up in Sigil.
There are a myriad of other choices. There is no need to ever get around to starting that book, you can spend the rest of your life evaluating the options for how you are going to write it.
