Agree with the other speculations that the culprit could be thrips. However, it’s inadvisable to use an insecticide or fungicide unless you know for sure what you’re treating.

It’s also very difficult in most cases to diagnose a problem from a couple of pictures, unless you can find some actual bugs and take pictures of them.

Best thing would be to get expert advice. If you have a nursery or plant store near you that you’ve found by experience to be reliable, you could take some leaf samples to them.

If you’re in the USA, I strongly recommend your local cooperative extension service Find Your Local Extension Service Office or Cooperative Agency

Outside the US, you could try calling the nearest botanical garden or university for their suggestions as to where you might get pest or disease ID.