Nu's find builtin isn't a GNU find repacement. I think what you actually want is ls piped into where:
ls **/* | where type == file
I do question the choice to alias a well-known program with a builtin that does something entirely different. You can also use ^find to avoid calling the builtin. I would've expected \find (bash-like) or command find (fish-like) to work as well, but alas...