In the third paragraph, it says “most Rails applications are developed on MacOS machines”, but any references to “MacOS” should be standardized now to “macOS” (as seen at the end of the first full paragraph).
Also seen on page 65 in the “General Recovery Advice” aside/inset - line 2 of the first paragraph (“using the recommended version of Rails and SQLite 3 on Linux, MacOS, or Windows.”)