This is one of the reasons it's crucial that the next set of secure messaging systems does away with tying real phone numbers to accounts. One phone gets compromised and the whole network is identified with their phone numbers.
Using any mobile phone connected to mobile network is breach of OPSEC, period. Even more in countries, where you cannot get anonymous SIM card. Not using phone numbers in chat app doesn't protect you against someone locating you. When phone is turned on, even without SIM, your location is saved, in inches. Thanks to 5G. And some phone turns itself on automatically, lol. Using laptop (without any wifi card) -> Wifi ca…
Signal is a desktop app, as well. Even if you wanted to run it on Qubes in a Faraday cage, you'll need a phone number to register to use the app.
In the ideal situation, no one would be using Signal, phones or computers, the design of the internet is inherently identifying and non-anonymizing.