I use an AC-1200 USB dongle with mt76x2u loaded driver. It allows me to get a beacon report, but this report is always empty.
wlan0: BEACON-RESP-RX 00:xx:xx:xx:xx:xx 62 04
Actually it should be something like this
wlan0: BEACON-RESP-RX 00:xx:xx:xx:xx:xx 62 04 [binary code written as hex...]
I tried it with a Nexus 5X and it works fine. So it has to be some driver issue.
Where do I report that stuff? Can somebody confirm that mediatek driver implementations of 802.11k do not work?
Edit: The driver seems to load mt7662.bin firmware. I can not find the firmware files? And looking in the driver, it seems not to be some kind oft softmac. Everything seems to be handeld in firmware. 
And the firmware is 5 years old.
Nope the firmware is from 2017-02-17.
Okay mode 2 is working.