Ive not tested max hr yet, going by online calculators (i know not accurate) its around 180-182
I got 168 on the test
I've looked on the laptop, easier to see workouts. I found you on Strava
Looking at your recent ride you hit 156 bpm for the climb- That will have to be your max HR, unless proven otherwise.
The 2*20 was in erg mode. with an ave 136 bpm for both intervals.
If you are unable to maintain a cadence of 85 rpm at around 136 bpm you need a fair bit of riding at lower intensities but with higher cadence to build up your cardio side. It may be you're a grinder(low cadence), which is fine, but it wont bring on your overall fitness- there is only so much force you can push through the pedals for so long.
Do a free ride on a flat-ish course like Tempest fugit or Richmond, set difficulty slider to around 10-15%. This will flatten all the hills to lower gradients.
Ride for 1 hour at around 85rpm with a HR monitor and report back. keep coming down the gears to achieve the rpm level
I'm not interested in what power, more you can hold this cadence at lower intensity.
Get you HR to around mid 130s for some of the ride and try for a 10 min period to get to mid 140s at 85rpm.