Signal doesn't run in a vacuum. It's main distribution platforms are app stores from Google and Apple. And most people are going to use stock smartphones from these two companies to sign up to Signal. But with them being under the same US jurisdiction, matching the two identities isn't that far-fetched.
The parent companies of both OS platforms are well known to funnel data and notifications to the US government. It too had no evidence to support it, until they admitted it. There's a setting for it now, but the person you're talking to might not be doing the same, so it's still out for profiling.
Other thing, they vehemently oppose F-Droid because "f-droid security flaws" bs, even though they can literally host their own repo for it without anyone else building their app. They would control every aspect of supply chain, but they didn't.
Besides that, they make it very inconvenient to get it from elsewhere, even though they did the bare minimum to provide a standalone installer, after an outcry. And with those stripped down installers, you have to deal with inconsistent notifications, because no apple/google. And they never ever gave unified push a look. I wonder why? Are they a small indie company with just a couple of devs?
Signal protocol may be "secure", but it's only a part of a bigger picture.
It's forced reliance on phone numbers, privacy averted platforms and unwillingness to work with opensource platforms and standards that lets it become decentralized and out of the hands of authoritarian government, leaves a lot to be desired.
Facebook's whatsapp also uses the signal protocol, but would you call it private or secure after all that zuck has shown to do? Signal creator literally helped them implement it too. I wouldn't touch a Facebook product with a 10 feet pole.
And now he's helping them again encrypt Meta AI, whatever that means. Why is he working with one of the worst offenders of privacy?
If that doesn't tell you these things are concerning, you do you.
"Tricksy little scrooges, they stole it from us."