Is that normal with xbox?

So with the dirt or whatever that is, it's only on the right

Why should dirt in the controller be normal?

Have been mine for 2 years and there's no dirt in it.

Happens. Just get out regularly.

What is the best way to do that?

Wet wipe and toothpick, at least that's how I always did it with used controllers.

Is this normal with Xbox?

Nope with dirty and sweaty hands.