I'm happy you found something useful in my post. There is another stair exercise that I just hated at first, but it was important in building strength and stability in the knee so that it can take your weight when coming down stairs. Maybe your PT has already got you started on this one.
Standing just one step up from floor level on your TKR foot, turn so you are facing the wall or the railing if you have that. Your TKR foot will be close to the edge of the step, and you will drop your good foot to the floor. You can put both palms on the wall, or hold the railing for stability at first. Dip/bend your TKR knee, and try to tap just the toe of your good foot on the ground below the step before bringing it back up next to your other foot. Do the knee bend 10-15 times. You are putting your whole body weight on your bent knee, just as you would walking down the stairs. You can put a large book or boards on the floor below at first, to make an easier goal to reach with your good toe. You don't need to put the good foot all the way down, just tap the toe. You also do a set of these facing forward looking up the stairs, and then a set facing straight down. These are hard and uncomfortable to do at first, but it gets better, and they are really good for building strength and balance on your TKR leg.
I can only say what worked for me, you may want to check with your PT person to see if they think these would benefit a person in your current phase of recovery. Someone still having a lot of daily knee pain and weakness may not be ready for them. Your PT person is your best guide.

@ddsack: I saw that heyjoe addressed the strength aspect of knee replacement recovery. You mentioned that you had trouble to get the flexion to improve. I did my own little twist on the heel slide exercise: once you did a few of them to loosen up the knee, keep your knee at the most “bent” position, as in pulled all the way up on the floor/surface, LIFT the leg, keep the bend, point the toe, and put it down. Toe first. Sort of where your heel was. Then gently lower the heel. It will give you a good stretch, and will get you used to that increased angle of flexion. Hold that position for a while, and repeat. It does really help to increase the flexibility of the post TKR knee. Better than pulling it in with straps etc.