They bought it for the metadata, not the message content.

I doubt that, the app very likely has a backdoor

https://www.kitklarenberg.com/p/signal-facing-collapse-after-cia

No. https://forum.hackliberty.org/t/why-we-abandoned-matrix-the-dark-truth-about-user-security-and-safety/224

Do NOT!! use sandboxed GMS & play store, if you need something proprietary, use aptoide or apkmirror, if you’re extremely desperate, use aurora store