We do not use Font Awesome 6. CB is still Font Awesome 4. We likely will not be replacing this until CB 3.x when we replace Bootstrap with Tailwind since I'll have to redo all the HTML at that point anyway it'd be a good time.

So you either need to keep both enabled or you need to be sure you're loading Font Awesome 6 backwards compatibility script, which I think might be included with core Font Awesome 6 by default now but I don't know if Joomla 5 is including it.

As for what we plan to replace Font Awesome with it's still undecided (probably heroicons ), but ideally a more stable icon library as Font Awesome changing icon names every major release is too problematic for us.

Then you'll need to have a Font Awesome account and use their Kit feature to generate a new Font Awesome 6 that includes FA4 and FA5 backwards compatibility font names. Then replace Joomla's with that. You can then turn CBs off.

My instructions were intending for you to download the files and store them locally in Joomla. You'd be replacing Joomla's fontawesome entirely. I believe Joomla has a means to do this using the resource manager to point to your own fontawesome to avoid override issues during updates.

Aside from that yes you'll need to unfortunately load both. It's just the consequence of a icon library deciding to rename classes with every major release. I don't have the time to keep renaming icons and breaking UIs. We strive to provide stability with our products and fontawesome is the opposite of that.

We likely will be done with font icons in CB 3.x and never have to worry about CSS names for them again. Since we'll have Twig for our template engine we'll just switch to using SVGs for our icons instead of hiding them inside of CSS. This will let us use fragment template files for SVG icons for easy inclusion throughout CB. Icon fonts are also just bad for accessibility as it turns into complete gibberish if a screen reader decides the parse the font.