Some exercises that you can do for great glutes even though your knees aren’t great are the following.
Glute Bridge holds as even though the knees are bent they are held in that position and you can keep squeezing the glutes.
Abductions and adductions using the machines as well as on your back using the bodyweight and slow movements of the legs being straight going inwards and outwards. And also on your knees doing the same thing and if very strong from a push up doing so.
Good mornings and Romanian deadlifts where you hinge the butt back pushing it out and then as you come up you push your groin forward and in so you essentially straighten up and then go down with me this is very effective for the hamstring and fullness of the upper part of your butt.
This will give you great head like shape at the top of the bottom.
Shoulder presses using your arms only but gripping your feet into the floor.