I have a FD lens and a Nikon Non Ai lens, with two adapters respectively.
Attached the FD lens to EOS M, set to M mode or AV mode, the aperture is fixed 00. Press the shutter button, it doesn't fire.
How to use these vintage lens on EOS M?
In Custom function menu: C.Fn-7 Release shutter without lense: on
The shutter can release.
It can shoot in either mode, including P, AV, TV, M. In TV mode, set ISO to auto. ISO becomes a variable according to time and aperture you set.