Just adding my support here for an EPUB output facility in Affinity Publisher, but not limited to reflow text. There are a million tools that will do the basics.
Affinity Publisher is a great tool for more visually focused and complex publishing, yet has minimal ability to output. Even the PDF export does not allow for using the Interactive PDF standard, so you loose the page spreads when bringing into Google's Play Books.
If you're making a comic book for publication, or a cookbook or any other kind of book where the layout is critical to the presentation, the fixed layout EPUB standard is what you need instead of reflow. Converting PDFs to EPUB Fixed Layout is currently done by hand by publishing houses. It's a mess.