Yes, it is now possible!
After a long wait, Apple finally enabled a Web based upload platform which everyone can use. You are no longer required to use a Macintosh/Apple computer to publish with Apple Books! This is very important for many authors who are not with Apple’s ecosystem and it is now very easy for everyone to go it alone with all Top 5 retailers WITHOUT using a third party aggregator.
Previously, and for a very long time, you could only upload to Apple’s bookstore using Apple software (iTunes Producer; free), which only works on Apple computers (not available for iPad/iPhone or any Windows or Google devices).
Here the link to publish/sell with Apple Books: https://authors.apple.com/epub-upload
Please contact me directly if you need any help or advice.