Sourdough starter should and sometimes does have a slightly sour smell too it and if it does then it's likely okay.
If the sourdough starter smells really bad and really sour then it is probably bad and should be thrown out.
But having a slightly sour smelling smell to the sourdough starter is normal and does not mean it's bad.
Sourdough starter will also sometimes start taking on a more sour smell when you haven't been feeding the sourdough starter enough.
So you may need to start feeding the sourdough starter more often if your sourdough starter is starting to smell more sour.
It can smell slightly sour but the sourdough starter should not smell really sour.