Who do you want privacy from and why?

That's not a rhetorical question. It matters. If you want privacy from corporations and governments doing mass surveillance because you're against mass surveillance in principle, Signal is great! As long as you don't give janky apps permission to read your notifications, or you limit what Signal shows in its notifications, your device won't leak to those kinds of threat actors. You can't be sure everyone you talk to is as fastidious though.

If the cops, gangsters, or similar are likely to target you and the people you're talking to directly, there's a good chance just using Signal without a security plan won't keep them from getting the contents of the conversation as in this recent incident where the FBI extracted deleted messages from notification logs. To defend against that specific attack, everyone needs to configure Signal to keep message content and contact details out of the notification. Dedicated devices for secure communication set up by someone who knows what they're doing are ideal in this situation. Signal is still a good choice here, but Signal alone won't guarantee privacy.

If you're being targeted by an intelligence agency from a rich country that has allocated a significant budget to surveil you in particular, you're probably screwed. There's plenty of public information about how US government officials and contractors are required to work with classified information to get a sense of how you might try to mount a defense. It's guaranteed to be inconvenient.