Local files can be converted with the html.to.design Chrome extension.
However, you will need to activate the permission
Allow access to file URLs for the extension to be able to convert local files.
After having installed the extension, activate this permission in the extension’s settings (either through Chrome’s menu or by manually going to:
chrome://extensions/?id=ldnheaepmnmbjjjahokphckbpgciiaed). Make sure the following toggle is enabled: