Also, I've seen a surprising number of DRM free novels turn to itch.io if you are looking for a "non-traditional" approach, but someone to handle a lot of the "storefront basics" for you. This seems to be an extension of itch.io becoming a major hub for indie TTRPGs, because a indie designer can just throw a simple PDF (and maybe a DOCX or an EPUB) on itch.io as opposed to the effort that DriveThruRPG/RPGNow want in PDF formatting. Then a few TTRPG related novels started using the platform, and like I've said I've seen a surprising set of novels that aren't even directly game related at this point. itch.io's flexibility in what they will publish/host is an interesting strength (though makes it a bit more caveat emptor than a traditional retailer from a consumer side searching for interesting books).
1. Smashwords[1]. They've been around for a long while now, and the publishing system isn't as snazzy as KDP. You input a Word file (.doc, not .docx) and - assuming their "meatgrinder" accepts your document's formatting[2] - the site outputs epub, mobi, pdf, rtf and various other minor format versions. The book then gets published on the Smashwords site.
2. More importantly, Smashwords has a number of partnerships in place - key ones being Apple Books, Kobo, and Barnes & Noble. This ability to ship directly into Apple Books is the MAJOR reason why I continue to use Smashwords as that's where the majority of my 'sales'[3] happen.
3. You can then download the epub and mobi files and upload them to the other two mainstream channels as followup actions: KDP for all Amazon/Kindle distribution; and Google Play Books for the all-important distribution across Android devices.
4. For the cherry on top, I sometimes also offer books in hardcopy. KDP has (I think) processes in place to convert an eBook into a hardcopy book. But mostly I use Lulu[4] because they've been around for a long time, I like their publishing flow, and
[1] https://www.smashwords.com/ - Smashwords landing page
[2] https://www.smashwords.com/books/view/52 - the Smashwords Style Guide - I guarantee that you come to love-and-hate this book in extreme-yet-equal measures.
[3] https://www.smashwords.com/books/view/11163 - I have never knowingly turned down an opportunity to spam the link to one of my books. It's free. Enjoy!
[4] https://www.lulu.com/ - Lulu.com landing page
I believe ddevault published his Wayland book this way.