You're my savior!
I've been wasting all my afternoon and night to solve this, and finally the solution!
Thanks a lot!
For the records, I was using the M4 from usb on a macbook air, as my macbook pro 15" late 2011 broke (affected by the world-wide graphic card issues, thanks APPLE!!).
I followed your instructions to prepare the usb pen from the macbook air, but then I needed a computer where to stick the M4.
A Lenovo Thinkpad T420 did the trick!
To the other users in a similar situation: if it doesn't work straightforwardly, get in the BIOS, and set UEFI mode to "legacy only" or something similar.
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