Until now, I have avoided regular exercise except for walks, which are good. They are in the open air, free, and avoid crowds and gyms, which is important in the era of COVID-19.
But my wife has introduced me to an online exercise system I can follow at home, in my own time. It is graduated, so you start slowly and easily and build up your fitness and strength as you follow the program. After living with my knees for a couple of years, I am finding it easy to do and helpful in strengthening not only my TKR knees, but also my arthritic shoulder as it improves my fitness. I'm not overweight, but I do want to get my legs as strong as they can be now that they are fully healed. This program is clearly improving the strength of the musculature around my 2 year old knee replacements. I also feel it is strengthening shoulder muscles around my right shoulder and lessening the discomfort from osteoarthritis.
If you are well past your surgery recovery phase, you might want to search out fitness programs online to find one that suits you and that you'll follow regularly to gain strength. I really feel this is going to work well for me.