Are uploaded fonts viewable with public sharing?

I don’t believe so, unfortunately. I’ve had this experience where I opened someone else’s Figma file but the custom font they were using wasn’t installed on my machine. I think I remember all the text in the design defaulted to something like Arial or another system font, and I had an alert in the top right saying I was missing fonts. If you have permission to share the font with the people you need to send it to, I would do so when you send them the access to the Figma file.

Alternatively, if you’re on the Organization or Enterprise plan you could invite them as viewers to your whole Figma workspace (though this might be too much access than you’re comfortable giving). I say this because Figma let’s you set custom fonts at the Workspace level, so then there’s be no need for individuals to install fonts on their local machines.