The Wrong Filter
As you can see this is an early Leica Standard model with an anonymous 19mm screw-in filter on the lens. I hope it's obvious that the filter is wider than 19mm at the front and covers the aperture lever. That makes it difficult to use and harder still with a lens hood fitted.
You can see it better in the next two pictures.
Leitz made a gadget to allow you to change apertures with the lens hood on, I think/hope it's called a "VALOO". It was originally meant for the lens when used in an enlarger. Try a search and you'll probably find out a lot more than I can tell you.