First I know I’m supposed to start with a claim, and the claim I’d use would be “there have been no photos of space since this first photo from space was taken in the mid 20th century”:
You can look at that and convince yourself the horizon is flat. Obviously the Apollo mission photos debunk the claim right away and show Earth is round.
One could easily say however “Look at how Hollywood uses CGI to create photo and video of earth. All the photos and video you see today could easily be faked”. So I couldn’t talk him out of it (maybe he wasn’t even serious ... Read even more