Signal is good, but not perfect.

Clearnet possible, centralized US server, fone number registration. BUT: its encryption is state of the art, open source also.

You might consider

- using burner SIM number

- using over Tor

- using the hardened Signal Fork #Molly

The last but most important:

No matter what encryption or what app in general you use (hi to the #SimpleX fanboys!) you use:

- if you download your app from an app store like Google or Apple, your app should be considered to be compromised.

- if you use iPhone or regular Google Android you are compromised

- if you use a custom ROM like #GrapheneOS and you are a person of interest for 3 letter agencies: They tap your fone by your closed source broadband chip that is maintained remotely by your telefone carrier. ANY OS on your fone is just a guest system.