Font Installer Won't Open

When I click a .ttf file to install a font, it opens Clip Studio Paint instead with an "unsupported file format" error. I wanted to add it to Photoshop, and I can't install it. I've installed fonts before and this didn't happen, and as far as I know, nothing has changed.

I'm new to MacOS so the solution is probably simple. But Google is giving me nothing.