At first, I wasn't going to get into the discussion because some people think the length I go to makes me a paranoid. Some people seems to argue that because we used Facebook and Google before, it's pointless to try to stop since they already have your profile anyway. I actually didn't have an Apple device for awhile, but because of all the privacy issues that come up lately, I bought an iPhone again and reduced as much of my Google services dependency as I can. Yeah I know Apple isn't perfect either, and I can't be 100% protected, but still feel it's worth making some changes and choosing the company that value privacy more.
Personally I use AdGuard Pro, it let you add custom filters (user filter) which I use to block
facebook servers. It's a long list so I just use wildcard (*) and the domain names. It's not practicable if you're still using facebook in some form, but I don't so it's no problem for me. AdGuard also log network activities, although for the most part it doesn't always make clear which app made the request. Still, from this I found certain apps I use that make a connection to facebook everytime I run it.
I believe AdGuard stopped developing their app for iOS, but it's still useful for now.