Even State Department-funded Human Rights Watch admits that authorities combine legal and illegal methods to obtain convictions: https://text.hrw.org/report/2018/01/09/dark-side/secret-origins-evidence-us-criminal-cases
Combining dragnet surveillance with device hacking is intended in the design of both tools. Hence, State Department-funded Signal dupes you into handing over your identity as part of the population-centric mapping. In custody, your phone will be hacked when it is taken away if it’s important.
https://xcancel.com/hannahcrileyy/status/2034273723667161480#m
It does use deniable encryption, but that stops working as a defense the second they take your phone and copy all logs from your device.
And large group chats relies on how well you can vet participants more than it relies on encryption itself, and if they’re too large they may as well not be encrypted.