I have a knee problem that is with me permanently- but not on a bike. After a layoff or after 50 miles Or so- my knees do ache a bit. No problem- take the pressure off the pedals by changing down and get the cadence up a bit. Within a few miles- no knee pain again.

But I have done rides where I run out of gears and the hill is still getting steeper. I have no choice but to grin and bear it but it depends how strong the legs are. Plenty of training and I can do it. After a lay off and I can't. I do a leg exercise that strengthens the quad muscles around the knee. If the quads are fine- no knee problems.