This doesn’t really have anything to do with open source software. It’s more of a privacy topic. You can harvest as much data as you want and still be GPL.
You can control who sees it by how and where you post it. If you don’t want people to see it, just don’t put it on the Internet at all. Even sites with fine-grained privacy controls can have flaws that result in information leaks.
No, it’s the same on the Windows side. Personally I like to build a new one in parallel, then migrate. I do plenty of upgrades on desktops, but I don’t think I’ve ever done one on a server (except stuff like CentOS 7 to 8 where it’s not really that significant of a change).
Migration is the safe option, but if it’s a huge pain to migrate, I might do the in-place upgrade with a rollback plan ready if it really goes poorly.
I’m not sure what this guy is smoking, but I don’t want any. He talks about licenses being different from contracts, but there isn’t any significant difference. He talks about developers getting paid instead of releasing their work for free, but there’s nothing stopping anyone from doing this right now. Plenty of products offer business licenses separate from their copyleft licenses. Anyone who releases their software under GPL or whatever chooses to do that, because that’s what they want to do. If they wanted to make it only source-available, or to sell source access, they would have.