I don’t know why you keep making this false distinction.
Signal for Android is AGPL-3.0, which is about as FOSS as you can get.
Yet its default configuration is bundled with proprietary Google Play Services, which as it stands probably violates the AGPL. But that wouldn’t apply to them since they can license it as anything, but anyone else compiling it as is would likely violate it.
Not to mention the concerns that Google could very easily make those proprietary libraries siphon off your messages if they really wanted to, not that they would and it would be noticied immediately.