I have the same question, and the link above doesn’t work. I searched and skimmed through a lot of this topic: Introducing Font Awesome 5 and SVG icons
But likewise I don’t see a list to know whether an icon is in the core set or not. Can’t find any other related search results on the forum either.
Discourse uses the free font awesome icons. All available icons that can be used are found here. You may have to add some icons to the svg icon subset in the site settings. You can see what icons are on your site by adding /styleguide/atoms/icons to the URL. If this does not appear please check styleguide enabled in site settings.
Thanks @ondrej and @pfaffman ! I was familiar with the use of Font Awesome, and I knew I may need to add some new ones, which is why I wanted to know what was included. The Meta and Styleguide plugin links are both very helpful. Still having a bit of trouble figuring out how to add new ones in some (but oddly not all) cases, but I’ll make a separate topic/reply about that.