Assuming you can tolerate the app's green color, Coolmuster ePub Converter Pro might work well with other input formats, but using a .docx file from Microsoft 365, while the conversion was Very fast, the result was 3 columns of text that ignored the original line feeds -- instead of a few pages it was all just one long paragraph.
If it works for you, it might make a good portable app using one of the portable conversion tools, since the only thing added / stored in the registry is an uninstall key. Folders are added to (My)Documents, Users\ [UserName]\ AppData\ Roaming\, and Program Files (x86).