Can we normalize not laughing out loud?

One of my coworkers told a funny joke and I smiled and said "that's funny."

He said, "that is the universal response of someone who didn't find the joke funny".

But it was! I just don't laugh out loud often.

I conditioned myself to make some sort of noise when someone made a joke so I made myself say "that's funny". I don't know what else to do to show appreciation for making me laugh.

Let's normalize the fact that if someone smiles, with both their mouth and in their eyes, looking directly at you, and says "that's funny", they DO find it funny.