Can it handle nonfiction books?

Yes — narrative nonfiction (memoir, essays, self-help, business, most how-to written as prose) formats just as well as fiction. If your nonfiction reads as chapters of running text with headings, the formatter is a great fit.

Pictures are no obstacle: they carry into both the PDF and the EPUB, with controls for captions and for full-page plates. See How are pictures in my manuscript handled?

Two things worth turning on for nonfiction specifically:

• A table of contents. Fiction usually goes without one; nonfiction usually needs it. See Can I add a table of contents?
• Chapters and sub-headings in the ebook's navigation, so readers can jump to a section rather than only to a chapter. See Ebook settings.

Where it still struggles is reference-style nonfiction that depends on complex tables, sidebars, or extensive footnotes — see Can it format images, tables, footnotes, or poetry? For those, a dedicated layout program is the better choice.