I am going to go and grab this cable from Officeworks after work today Comsol HDMI 8K, 3m for $40. Doesn't explicitly state it is 2.1 certified anywhere but they claim support for 4k120 so I will have no problems taking it back to them if it doesn't work as intended. I've seen some reports on reddit of them working well so should be fine. I have a 5m $10 junker cable that has sat around for years that almost does the job too, works in 4k120 4:4:4 but the screen blacks out every now and then. So close yet so far.