After buying a second hand M, I quickly realized that the lack of shutter remote really annoyed me. Unfortunately ML+ mic trigger didn't cut it for me.
I then made this : https://www.thingiverse.com/thing:2524414
The 3D printed part fits on the EOS M and permits to send IR trigger signal directly to the IR sensor of the M.
To emit the IR I use a Wemos D1 Mini ESP8266 board and a 940nm IR led.