Worth separating two things that get collapsed: blocking network access stops transmission, not collection.

With the toggle off, the app still reads everything its permissions allow and can cache it locally. Nothing leaves while the block holds — that part works, it's enforced by the OS. But the data is sitting there, and the moment network comes back it can be flushed: you toggle it on to use a feature, you restore a backup, an update or a ROM change resets the setting. You've deferred the upload rather than prevented the collection.

Two gaps that toggle doesn't cover either: a blocked app can still hand data to another app on the device via shared storage or a content provider, and that app can send it. And blocking app A does nothing about the same analytics SDK sitting inside app B.

For icon packs and launchers specifically there's a stronger check than blocking — look at whether the app declares the INTERNET permission at all. An app without it cannot open a socket; the kernel refuses, no matter what the code wants. That's enforced rather than configured, so there's no setting to forget. Most icon packs are just resource bundles and need no permissions at all, so a launcher or icon pack asking for INTERNET is worth a second look.

One catch: INTERNET is an install-time permission, so it doesn't show in the runtime permissions screen on your phone. You'll see the full list on the Play listing under About this app → App permissions → See more, or with aapt dump permissions if you have the APK.