Several countries have recently blocked Signal, leaving their residents without a trusted and safe place to communicate. To help in this situation, Signal provides a built-in censorship circumvention feature and also includes support for a simple TLS proxy that can bypass these blocks in many cir...
It’s also the metadata. Profile and contact discovery is also private. I don’t think they have anything except your IP.
Seal sender is a nice idea, but since you can easily run timing attacks on centralised infrastructure it is pointless for Signal, or rather you have to trust them that their infrastructure is not compromised.
They also store device ids for push notifications via Google/Apple.