With anything that’s new I try to work back to ask “ what was changed”? For knees I’d be especially looking at the bike ( is it the same bike as usual), the cleats ( have you changed them recently, or are they worn, or could one have slipped) , is the saddle height still what it should be ( and saddles do sag significantly over time).
If everything seems ok, I’d try using Voltorol short term, or dynamic taping ( there are some excellent guides on YouTube)
Another consideration is the conditions you have ridden in. I’m a dinosaur, but also a qualified and experienced soigneur, and I stick with the 20 degrees minimum for shorts.
A commonly forgotten aspect of cycle position is the stance. The drive through the knees should be straight, which means of some riders, maybe with wider hips, setting the pedals out a bit ( some brands offer a range, extenders and washers are also used. Cavendish, for instance, uses a wider stance set of pedals. If a rider has multiple bikes, it may vary, especially if a bike has a triple chainset for instance.
If the issue persists, a visit to a good physiotherapist who understands cycling would be my recommendation. If one says “ bring your shoes with you” it’s a good sign.