Better yet, put no pressure at all on the pedal. Lift your leg on the backstroke. Legs are heavy, it is real work to lift them and this work will get your bike down the road. Let gravity take your leg down on front part of stroke. Gravity is always there. You cannot avoid gravity. You can make gravity work for you.

How do you think your leg comes up on the backstroke if you are not lifting it? It does come up. If you didn't lift it, it came up because of the overpressure on the opposite pedal . In fact most people are pushing down on both pedals all the time and doing major work to force the leg up on the backstroke.

The wisdom of the internet has long decided that something something psoas muscle and so there is no power to be had from backstroke. Disregard the internet. I have had chrondomalacia a couple times. It can be dealt with. Lift your leg and you can ride your bike even while the chrondomalacia is bad. Most of your weight can rest on the saddle. Riding should be less stressful than walking and less stressful than merely standing.

While you learn how to do this avoid hills. It is not simple to get up hills without a lot of pressure on the pedal. It can be done but feels unnatural and will take time to learn. When you begin to tackle hills have a real low gear available and resign yourself to going uphill slowly.