does it make sense to mark a function/method as

internal

so that it can be unit tested? or is there a better way to do it without marking it as internal or public?

I feel like this is going to turn into a debate on test scoping

Exactly as Shawn said. Unit testing does not mean testing every function/method in isolation. Only the public. If you test everything specifically, it removes your safety net for refactoring.

thanks. I'll refrain from making my method internal

it’s worth adding that if that method feels rather complex/as something that should be really tested. It may be an indication that splitting it off (and relevant data) into a separate smaller class may be a good idea

since it's supposed to be a "private" method, then nothing can trigger it expects the public ones, so prober testing the public methods which trigger it should be enough.