trying to make a near 100% foss build lol
Google, definitely. Microsoft sliiiightly less so, windows specifically you can turn off most monitoring and telemetry- though it would still violate the 100% FOSS idea since windows is technically proprietary
With Windows turning off telemetry will be an ongoing battle as updates find new ways to enable shit.
Technically android is open source, though. You could install AOSP on a device and not use any Google services
Except in reality nobody really does that. Everyone uses google play services / gapps because they pretty much have to.
Microsoft has been contributing a ton to FOSS the last 5 or 6 years.
Their flagship programming language, .net, is fully OSS and runs best on Linux.
You don’t even need to do that. You can side-load iOS compatible apps through the web browser. The device needs to either be in developer mode or provisioned with a configuration profile for the app (or app signing key) in question, iirc.
It’s quite a pointless effort, though - using an open source licence and having the source code publicly available is the best you should really try to get for iOS apps. But I’m guessing this is just a theoretical thought experiment.
I believe the iPhone uses a basic read-only protocol to access media. (MTP?) You can use iTunes to add files to the iPhone but that's not FOSS. I personally use Photosync, you might like that for wireless photo transfers.
