I read all of the info I could find on here before flying into Cancun airport. Thought I’d say thank you for all your good advice and confirm it worked!
1) I did my COVID test in my hotel and they emailed the results 3 days (the max) before my flight. I uploaded them on the United app in the Travel Ready Center. 1.5 days later/about 24 hours before my flight, United confirmed via text that my results had been accepted.
2) On my hotel WiFi the morning before my flight I did the Mexican health questionnaire here: https://www.vuelaseguro.com/home. I saved a screenshot of the confirmation and QR code on phone. This was readily accepted.
3) I checked in online with United and did not check a bag. I arrived two hours before my flight and did not stop at any of the United check in lines; went straight to security. From curb to my gate was less than 20 minutes. This was at noon on a Thursday. I was so earlier I snagged a seat on an earlier flight.
4) As mentioned by others here, you’ll see people holding signs saying you have to pay an exit tax. Haha. I took your advice and ignored it; you were right! No one asked to see proof.
Happy to answer questions if anyone has them!