Slide up from the homebutton.
My device is mx4 pro instead of mx4, so i think your approach does not work.
But i found my solution now.
I disable “hiding smartbar” in settings.
the smartbar appear and the three dots can act as menu key!
I have a Meizu MX Pro 4 with 22.214.171.124 U version.
may i please know how to “hide smartbar” from settings ? i did not find this settings anywhere ?