I read this article Beware the faux bold (and how to fix it) by Richard Rutter which explains how we, as developers, can help prevent the faux bold by properly linking your font files to your @font-face rules. But as a consumer, our experience is dictated by developers who mostly don’t care about this.
However, we can modify our experience via Safari’s user stylesheet! You can add one by going to Preferences > Advanced > Style sheet and importing a CSS file that contains the following:
* {
font-synthesis: none !important;
}I typically save this file in my iCloud Drive so I have access to it on any device but one can easily use ~/safari.css.
This will disable all font synthesis rules but I’ve found the faux bold experience is worse to have than one crafted by a thoughtful developer.