I think it depends on the design.
I have very bad knees and feet (two surgeries and counting), and I’m 52, so I don’t look challenged when I’m sitting. (I think people can tell by the pronounceed limping when I stand and walk that something is wrong.)
In most churches, the kneelers tuck neatly under the pew and I can stretch my feet and legs out and wiggle them to keep them from freezing up.
In some of the older churches, the kneeler is in the way of my feet (people must have been shorter and smaller back then!), and so I will sometimes use the kneeler as a rest. I try not to put my shoes on the kneeler, but sometimes you have no choice. If the alternative is falling when I stand up to go forward for Holy Communion, I’ll rest my feet on a kneeler.
And sometimes, parishioners in the pew with me will put the kneeler down at the beginning of Mass to pray, and then leave it there. I’m sure they must have arthritis in their hands or something that makes it difficult to move the kneeler, so they just leave it. But this is very uncomfortable for me to sit with my feet tucked around a kneeler, so I usually move. But if I can’t move, I’m sorry, but I will have to rest my feet on the kneeler.
I really like the way our Perpetual Adoration Chapel is designed. There are kneelers, but two of the pews at the side are built without kneelers so that those of us who can’t kneel can still adore the Lord reverently. I wish that more churches would do this–add a few pews at the side with no kneelers for those who can’t kneel anyway.