Is there any way to view private favorites?

I’m curious because I’ve just started using this site not too long ago and I’m slightly paranoid that they still may be viewable through Danbooru’s API or another middle man.

I would just like to know beforehand if there is some exploit like that existing at the moment, thanks.

No, there's no known exploit like that, and the site is in very active development, so if such an exploit was found it would be promptly fixed.

Favorite groups can be made private too, but they are created as public, so make sure you edit them to make them private if you want everything to be hidden.