I have to admit - Expanding Earth is hard to debunk!
I think because like Flat Earth many of the observations and elements therein are accurate - they just get the overall picture wrong.
Like stealing the ball with 4 sec left running down the court no defense in sight for the winning layup and missing - comically bouncing off the backboard.
Alas, I believe most crackpots mean well, they just aren’t very good at the sport
Likewise, flying in a plane for any distance and seeing the course is identical to if you pulled a string tight against a globe (give or take). I suppose pilots could choose to fly in an arch to keep the secret, but eventually some capitalist has got to spill the beans to cut costs, right?
Also: the southern hemisphere.
It doesn’t really matter if the earth is flat or not, for them it’s about being part of a community of people who believe in something that society tells them is wrong. There is no changing minds besides the 1 in a million you hear about and so all the calculations you could do would never work, sadly.