What's the deadline to file my 2019 tax return

You have missed that deadline.    If you were getting a refund, it has been forfeited and will not be paid.  If you owe tax due, you still need to pay and you are subject to late fees and interest, for which the IRS will bill you when they receive your mailed tax return and your payment of the amount due as shown on line 37 of your Form 1040.   The only way to file a 2019 return is by mail.

In answer to your question about "when" the deadline was---it was July 17, 2023 -- or October 15, 2023 if you had an extension.