Relative adverb or Interrogative adverb?

I know a place where we can eat out.
I know the reason why she did it.

I have learned that where and why are called relative adverb but I was wondering if we omit a place and the reason like

I know where we can eat out.
I know why she did it.

Should they be called relative adverb or they here are just interrogative adverb in indirect question?

I know + where can we eat out?

I know + why did she it.

And I am not sure what it is.

I know how we can solve the problem.

Here how functions as a relative adverb or an interrogative adverb?

I think that whichever it is called, it is okay and there is no meaning difference. What do you native English speakers think?

Thank you so much as usual in advance!