After you file

I am not sure what boxes you saw in the program but you have never been able to mix tax years.   Since the IRS is matching the W-2 info the employer sends you and what you report on the return are cross referenced.  Since the IRS has stopped your return in processing then that is what they must be doing and they will most likely find and correct your error.  Do NOT amend the 2019 return until they are done reviewing your return.