Fonts will not download - macOS Big Sur (version 11.5.2)

Hi there, hoping someone can help/give some clarity.

I am trying to install two fonts from a client, and they are not showing up in the font book. I have tried everything, going through the folders, downloading and extracting the folder differently, adding through the guest profile, restarting, deleting cache, and nothing works. I add to font book, validate them, click install even though there are warnings, and it doesn't come up.

I know it isn't the font because I can download it onto other computers that run Catalina and a Big Sur 11.5.1. So is it my computer, or is it the current version of Big Sur causing me issues? I also wonder too if my computer is doing something to the files when I download them?

Any help would be greatly appreciated!