After a recent new growth spurt, many leaves, old and new, are turning yellow.
Camellia Leaves Turning Yellow
Certified GKH Gardening Expert
Yellowing leaves is an indication of plant stress, such as overwatering or pests. I would check the soil to make sure that it's not too moist. Also, check for any insect pests. For more information on what causes yellow leaves and to help pinpoint the cause in yours, this article will help: https://www.gardeningknowhow.com/plant-problems/environmental/plant-leaves-turn-yellow.htm