C-mount lenses are not an option. Been there, tried some of them. Very low quality optics made mostly for security cameras or machine vision that don't do justice to crop mode resolution
Simply skip them and don't waist your time and money.
Not many wide angle lenses for crop mode, but still some:
Fish eye lenses:
Samyang / Rokinon 7.5mm f3.5 - 190gr 250$
Samyang / Rokinon 8mm f2.8 - 260gr 260$
7Artisans 7.5mm f2.8 - 278gr 140$
They all will give you angle of view equivalent to 24mm-28mm FF after correction in Davinci Resolve and do exists for EOS M
Regular / rectilinear lenses:
Laowa 7.5mm f/2 MFT 150gr (Lightweight Version) / 500$
SLR Magic 8mm f4 130gr / 140$
Both are made for drones as one of main applications. Laowa is rectilinear and near perfect - sharp wide open, f2 aperture. Could be used for night shots. But relatively expensive.
But both are
Micro Four Third lenses only. You'll have to find somebody to change the bayonet for you to Canon EOS M. And this will cost you even more money. A local guy have done this for me for many other lenses but decided to buy a better camera and abandoned the project
For scenery / landscapes used mostly Canon 10-18mm with regular adapter. 35mm FF equivalent angle of view which is my favorite. But drones typically use 24mm-28mm.
