It's not a CIA op or something. It's just anti-semitism.
Vatican II included a stance of not blaming jews everywhere for the death of christ and opened itself up to the ideas of other religions and science.
This ended up leading to an apology for the persecution of astronomers such as Galileo and Copernicus years later
They use the flat earth thing as a dog whistle for wanting the Catholic Church to go back to its old ways.
That's all it is. It's just trad cath fascists jerking themselves off and some dumb guys following along not realizing what they're doing.
I thought modern flat earthery originated with Protestant-style Americans
The Principle was the movie that sent it into the mainstream and the guys behind it are trad cath fascists
https://en.wikipedia.org/wiki/The_Principle
https://archive.org/details/ThePrincipleDVD2014720p