Yes, you can achieve 20 micr size particles using ball milling.

You can as well as dry, also as wet grinding. Wet grinding is more efficient. In the laboratory scale, it is simpler in a ball mill made of porcelain with porcelain or corundum balls. Ball diameter 10-20 mm.

Any specific model ? Eg. Fritz Pulverisette.. I need about 20 gm.

For 20 gramms of powder it is enough a simple agate mortar like this:

https://lavallab.com/products/crushers/agate-mortar-and-pestle/

https://www.lemke-laborbedarf.de/moerser.html