Thank you, Teacher Pi, do you mean only after getting new I-797

thank you, Teacher Pi, do you mean only after getting new I-797 can I go back to China? when I get petition receipt, I cannot go back?

I know that a person can start to work for new employer when getting petition receipt , not approval notice (I-797), but you seem to mean only after getting the final I-797 can I go back, in that case do I need any kind of employment verification letter since I have not started in the new company?