Even if you could convince a flat Earther to go to space, I suspect the vast majority would not be swayed.

As you suggest, they’d instead likely say that it’s all fake trickery. Even if you gave them a space-suit, put the helmet together right in front of them showing no electronics of any kind, and let them walk outside, they’d still say it was all fake trickery.

They would never believe their own eyes, because they’ve already made up their minds. An allusion to the Earth being round is an illusion.

You don’t even need to go to space to prove the Earth is round. As @Pons_Aelius already said elsewhere in this thread, there was even a show made and funded by Flat Earther’s to try loads of different tests, and they ended up rejecting all of them because they accidentally demonstrated that the Earth had to be round.

Their mind is already made, and they’ll only accept results that conform to that belief. Anything else is either fake, trickery, or flawed.