I mean, there is always a root for the trust. In this case, the root is Apple. Signal is one leaf below. Compromising root compromises everything. In this case

I mean, there is always a root for the trust. In this case, the root is Apple. Signal is one leaf below. Compromising root compromises everything. In this case, root being the device and OS, it has unrestricted access to everything happening by your actions. The data you see on your screen is processed by the CPU, developed by Apple, controlled by kernel, coded by Apple. The can access everything they want.