My own take is that humor is no more or no less appropriate in a novel than it is in life. If a novel is to realistically portray life, whether past, present, future or imaginary, then humor should appear as frequently or as infrequently as it does in life.
I don't think it matters whether you are a funny person or not, the same as it doesn't matter whether you can write about murder without actually being a murderer. What matters is whether you can see humor, even in the unfunniest of situations. How many times have you heard someone say, or perhaps said yourself, "God must have a sense of humor"? That's because something oddly or darkly funny has just occurred.
If readers have to know you to appreciate your humor, what else must they have to know about you to appreciate what you've written?
Granted, humor is extremely difficult to pull off. But I think it's definitely worth the effort. You may not be reading books that make you laugh out loud, but you undoubtedly are experiencing or observing situations in your life that do.
My historical novel is about slavery, about as unfunny a subject as there is. Yet the story is filled with humor, practically every kind of humor: slapstick, puns, witty statements, and crude, obnoxious remarks. Some of the humor, I think, will make you laugh and then feel embarrassed or guilty that you did.
The beauty of humor is that it not only can provide "comic relief," it can capture the basic makeup of a character by showing how they use humor or respond to it. They could be the person making a joke or they could be the butt of a joke.
Because humor relies on timing, I think it's one of the best exercises there is to hone your skill at the rhythms, beats, and overall sound of your language.
If you're not proficient at it or not comfortable attempting it, the question then becomes whether you work at it or give up on it as being beyond your grasp. If you choose not to give up, I think the road to using it and eventually mastering it starts with baby steps, like a natural response to a question or situation that is unexpected but very funny.