The thing if someone has memory access Signal doesn't need to store anything, transiting data is now available. For example all of your contacts when doing contact discovery. It used to be a simple hash, something for which you could build a rainbow table in a few hours, at the worst. It's lightly better now, but still.

Don't take it from me, take it from Moxie:

https://signal.org/blog/private-contact-discovery/

It also doesn't really matter if the software itself can easily be tampered with in memory by the hypervisor. Like I said, they are putting a lot of trust in Intel SGX.

And let's not even get into the digital sovereignty issues, and financing of right wing billionaires. Yes, running on AWS is an issue. It's multiple issues even.