On Android you can block trackers per app with TrackerControl.

https://trackercontrol.org/

When I start as a mobile lead at GiantNonTechCorpYouWouldKnow, I was looking at one of the two apps I would be leading part of, just to get familiar I looked at all network connections it made and found it called Facebook. I asked product team why we pinged FB given the app it just for our business; they had no idea we even did that, and it was immediately ordered the FB SDK be removed from the app. I never did discover why it was there in the first place.

Not on the ones I write, but I know that I'm an outlier.

From what I have heard, the FB SDK has a bunch of nice UI candy, so folks may have used it, just so they can get the nice splitscreen, etc. (UISplitViewController is a nightmare. I suspect that SwiftUI may have some improvements to offer).

Indeed, certainly makes application proxy filtering more of a must than a luxury for the wider consumer market in todays times. Though not sure (beyond rolling your own) what offerings are out there for consumers as focus seems to be VPN proxies.

Hence: Pi-Hole at home, and a on-device VPN that blocks 98% of all that crap.

I am sure they can still get some info and that some requests slip through but I wish them luck building a coherent picture of me by a few scraps of random info.

Yep, so much for the GDPR. Despite this, I'm sure someone is going to throw the "enforcementtracker.com" link to "prove" that enforcement is sufficient.