Yes, mail in voting allows more Americans to vote, making it less cumbersome for folks with limited wherewithal. A good thing, yes?
Why assume that "blue" precincts are more prone to cheat anymore than "red" precincts? Why assume that election officials and party machinery/poll watchers are not "on guard" in protecting the integrity of the election?
Have you ever volunteered to work at an election precinct? Why assume that Americans who work at election sites, and tasked with the responsibility of ensuring free and fair elections, do not faithfully discharge their duties?
Have faith in your fellow Americans who screen/count the ballots. Volunteer and see for yourself.
Edit: Link added
Link: https://www.pewresearch.org/politics/2020/11/20/the-voting-experience-in-2020/