iOS since at least 12 has been using it. Here's a blog post by Project Zero describing it: https://googleprojectzero.blogspot.com/2019/02/examining-poi...

And I also remember attending a DEF CON (or a similar conference) talking about how the keys used to sign shared library code is shared across all processes (including unsandboxed, privileged processes) and depending on your perspective, it could be a vulnerability.