Ok, so I have tried it with my (Windows) PC, and two different (android) phones with success with each one. I don't have a Mac or iPhone to test with, but I pulled out my old iPod Touch. Now I don't know about Mac (or what is going on with it), but with the iPod (most likely with any IOS device) you need an OTG adapter to use it; it was the same with my android phones. In other words you can't go from USB-C to Lightning or USB-C between mobile devices. You may or may not already have this in place, but just throwing ideas out there. Otherwise (the M0) simply tries to charge the device you are connecting to.
Think of the OTG adapter as a traffic director. It tells the phone to send data out, rather than let it come in. And since you can't charge the phone (incoming) at the same time you send data out (outgoing) that is the reason there is a need to have it in place.... If you already knew this, then disregard the above information, and please take no offense (as if you didn't already know).
As for the Mac, have you used the M0 as a DAC to it before? I can't recall if you have to install a specific driver for it to use the M0 with it or not, but all my other DAPs need one to work as a DAC on MacOS (but not Windows).