Is knowing how to solve code challenges and whiteboard interviews normal?

Nope. Programming is one skill
Cracking coding interviews is another skill.

Apparently it's common, I've never faced it personally, nor do I bother with that style when hiring someone.

That kind of thing should be only used to weed out juniors from wannabes anything mid to senior usually comes from your cv and work history and the side projects you may work on.

I like a dev who has a couple of open side projects, you get to see the work that they actually like to do and enjoy.

Kinda. Get one of those programming interview books. Keep it around every time you switch jobs because that's the only time you'll ever need to do anything similar to what you'll do in the interviews.

I recently had one of those. Didn’t feel like the challenge was too far off what I'd usually do and the whiteboard interview actually had something to do with the architecture they're building. I got the job with no prior experience doing those interviews.