Are brown dwarfs considered to be dark matter?
No. They are low mass stars, very cool in comparison to the Sun.
They call them brown dwarfs because they’re small and don’t give off nearly as much light as the Sun. Thus, they are difficult to see. Even with our largest telescopes, it could be easy to miss a nearby brown dwarf. But they are made of the same stuff as the Sun: hydrogen, helium, etc.; i.e., not dark matter.