Ongoing knee issues mean that dealing with my knees pre-season is my "normal", unfortunately. Hopefully one day this won't be the case. So for me, the past two seasons, my problems and difficulties lie around getting my leg muscles strong and balanced to take the pressure off my knees. My knee issue is bilateral chronic patellar tendinosis (worse on one side - now that I think about it, worse on the side that my ski turns are also worse on....).
....as my fitness and leg strength increases and the burning in my knees decreases.
Another way to take pressure off the knees instead of building massive quad strenth, is to stand up taller. You,
@fgor, unlike so many newish skiers, keep your ankles flexed forward to maintain tongue-shin contact. Good for you! This is a remarkable thing; most skiers open their ankles and lose that contact. You keep it. Big advantage to saving your knees.
Accompanying that strong continuous dorsiflexion (I do this, but not everyone does), is your race stance. Your knees are bent and you are bent forward at the hips, so that your thighs and torso are very tilted. At the speeds you are traveling, such a dramatic low stance is not that needed. You could open up your knees a bit and open up your hips to get your thighs andtorso more upright.
You'll get two benefits. First, your knees won't have so much pressure on them and your thighs won't have to exert so much effort so building high quad strength won't be so essential. Second, your balance will be fine because of the closed ankles. You won't be pushed aft by standing up at the knees and hips, because you are simply raising your CoM, not moving it fore or aft. You'll have more up-down range of motion to use for suspension when encountering lumpy snow.
Since you are good at keeping those ankles closed, you could give this a try and see how your quads feel at the end of the day. The burning may disappear. I used to have that quad burn and hot knees, and the endorphin rush after skiing that dealt with the quad pain. I thought it was a sign of skiing hard and skiing well. Now I ski with much better balance, with ankles closed, and the burn never ever happens. I wish I had gotten rid of the strain I put on my knees earlier. They don't heal up in the summer now like they did years ago.
There are people who will insist that their balance is better if they open and close their ankles. I think this is true for them. The difference between people who do and don't open/close ankles must be in anatomy and gear. So know this: I am not saying this suggestion will work for everyone. But it may for you.
