For fitness and recreation, perceived exertion and tracking day to day with a fitbit or something is plenty.

If we're talking actual bike training, we're not in the ballpark yet.

It's age and genetically dependent. If you're deemed in fair enough health by a physician, then you acquire the max by doing something like a 2 minute hill sprint interval. All out, die at the top or before the top.

My max is in the low 190s and I'll hold 170's and finish the last 6min or so of a 20 min power test in the low 180s.

85% is steady state power output level, ie...cruising solo for a couple hours in mild discomfort (160bpm = 85% of 190).

I think sometimes early on in riding bikes, max HR and a HR you can comfortably hold is very trainable. Like in the first few months. After that, not so much. After that it's your tolerance for lactate and how quickly you can clear it. You won't be able to increase your max HR and your HR zones after a fair amount of training, just the physiology itself.