The advertising statements from Signal don't help at all.
85% of the SP run on Google's Android and that sends encrypted data packets to "home" every day. No one knows what's in there, but can assume that Google can assign the IPs to fixed users every day.
If someone sends a signal message Google knows where it comes from and they know to 85% who got it!
All this results in valuable meta data!
Proxies are useless, because they have your proxy IP / VPN IP, ect.