Signal doesn't collect IPs and therefore can't even hand them out. It's been requested in 2021. Here's a list of requests from authorities they were allowed to publish. I've looked through 3 of the most recent and nowhere do they reveal IPs.
Despite their claims of total privacy, I imagine, like any software company, they have full access to their own back end including encryption keys and server logs. Meaning they can and probably will moderate their own platform if there is enough pressure from nation states/IP owners.
If you don't put trust on someone something, you left yourself to trust and do all the works. However, you don't trust yourself either, sadly I can't offer any solutions.
TBH I would just use email over TOR and encrypt communication with PGP. Rotate identities every now and then and you should be fine. Yes it doesn't have forward secrecy but it removes the effort to find the "right messaging" service and is instead ubiquitous (and you can sign up for anonymous email addresses online too, which makes it even better).
That won't stop people here shitting on Signal and repeating that they collect IPs indefinitely. Lemmy seems to have an anti-signal agenda for some reason. Idk why.
Arguable in it being "the best app for privacy". Can you link to a source which shows that phone numbers are not linked to accounts? (Why do they need them anyway?)
They have published requests from the law enforcement and their responses to these requests. The only unencrypted data they have is the phone number, a date of sign up and a date of the last login. That is it, everything else is encrypted and they cannot access it whatsoever.
You also don't need to show any ID for a business to meet "know-your-customer" regulations. Can you get a phone number without revealing your identity?