It goes even further sometimes, I've seen someone in the Go community slack announce they are going to dial back their activity because of Very Serious Clauses in their Apple contract.

That seems to imply that Apple employees are prohibited from being good internet citizens and e.g. helping people out with any kind of software issue. This presumably includes contributing to open source, although I'm sure they can get approval for that. But the fact they have to get approval for it is already a chilling effect.