Hi, maybe a bit late but the latest version of python-broadlink indeed does not seem to be able to put RM3 mini into learning mode. I use version 0.7 (https://github.com/mjg59/python-broadlink/commit/8d3c9f1e9f7ad19f1c054ca3278670c8c9ea0eb1) and it works fine.
I hope this helps anyone.