Hi, and welcome to BoneSmart!
but only find reference to very fit people regaining fitness by extreme exercise
I don't see only people here who use extreme exercise as you mentioned; I do see many people who have lost mobility due to knee issues, who need advice on how to regain strength and function after surgery. BoneSmart doesn't promote extreme exercise after a TKR or PKR; on the contrary it's a more gentle approach to recovery that's promoted. That doesn't mean we suggest patients become couch potatoes; rather that they start off just doing activities of daily living, and gradually progress to more active lives like they were living before they had knee problems and knee surgery. There are some patients here who post about their strong exercise-oriented recoveries, and we cheer them on when it works for them, but for the most part BoneSmart advocates a "kinder and gentler" recovery progression, so to speak. We don't advise "enforced inactivity", rather a phased progression of activity that allows your knee to recover from surgery, but doesn't overdo and cause more pain and swelling in an already stressed knee.
If 10000 steps is too painful for you, maybe you need to rethink that approach for now. It is only five months since your surgery, and you're needing surgery on your other knee due to problems there also. I would do whatever your knees allow you to do without causing too much pain, and allow the surgical knee to continue it's recovery while not stressing your other knee too much.
I think that once you have two good knees, and they're both recovered, that's the time to begin to strengthen them again. Right now it seems to be causing you more pain than you can take (as is normal with knee issues). You're in a double quandary with one knee recovering and the other needing surgery, so I suggest listening to your knees and if they hurt too much or swell, etc, back off until you find a happy medium where you can continue to recover the right knee while not stressing the left knee. It's a hard place to be, I know. Just know that you're not alone, and people here will support you, and care about you and your journey. Please, keep us posted and feel free to ask any questions you have, we are here for you!