Obviously there is the disk encryption passphrase at boot, adding another one for signal would in my case be redundant.

I also have full disk encryption, but I still have some databases on my disk encrypted because I decrypt my disk when I boot my computer. But yeah if you have Signal open (& its db decrypted) all the time it would probably be minimal. I don’t have Signal open all the time though, only when I want to check messages or am actively using it

I don’t think it does much on the typical desktop, be it windows or linux, where there are so many ways to escalate or persist privilege for anyone that has user-level access.

The point would be encryption, even the root user wouldn’t be able to read encrypted data if they don’t have the passphrase