I’m aware that multi-site exists but I’ve never used it.
Could I use it in a type of reseller mode, where I ran one install of WordPress but provided completely separate sites for separate users? Such that the users didn’t even know the other sites existed, they just saw their site?
Every time I search I keep finding articles about the opposite: letting users work across multiple sites, not keeping them inside one site.
Read more here:: Can you have multi-site WP and keep users separate?