I feel post pandemic children are reacting in several different ways to the new atmosphere. I feel that we should not use labels as "shy" too early. You can observe a child a little more in school, home and outdoor settings too.
Next Steps
Few steps that can help you are:
1. Speak to the child more about things he likes.
2.Encourage him to talk about his day at school ( get him started by telling about your own experiences, ask him what he likes, does not like)
3. Given the age of the child, reinforce small good behavior actions too by appreciating it.
4. Arrange play time for him to interact more with other kids.
Health Tips
Be cautious that if we give too much attention to a good or bad trait ( eg: shyness), it increases in children .So try to normalise the situation and help him cope gradually .