You asked
Is the leica summilux m 21mm f 1 4 asph hard to focus manually?
The Summilux-M 21mm f/1.4 ASPH is manual focus only, with no autofocus, so you'll be setting focus yourself every time. I don't have a rating for how hard it is to focus, so I can't say whether it's easier or harder than other manual lenses.
It's also wider than the rangefinder's frame lines, which means you'll need an external finder, live view or an EVF to see the full frame. Those tools can help with focusing as well as framing. You can see the full list of Leica M bodies it fits on the Leica Summilux-M 21mm f/1.4 ASPH page.
Written by Claude from this site's pages.