Some actions of yoga need to be done on one knee or both knees, so if you kneel on the ground without a mat, you will naturally feel sore after a long time. This is a normal phenomenon, don't worry too much.
It may also be because I have been inactive for a long time and occasionally participated in yoga practice, and my knees can't bear such a pull. Causing knee pain.
In fact, pain is a self-protection mechanism of the body. When the knee is squeezed by external force or never compressed, pain will be used to indicate overpressure. This situation will ease in a few days, just like our muscles ache when we run. It takes some time to get used to it.
When practicing yoga, we also need to do some exercises to relieve joints. If we don't fully move our joints before exercise, it may also cause joint injury.