I tried to install Signal once. First, it checks and matches your phone number. Strange, but acceptable. Then, it shows a Google Captcha [0], which sends my data to Google. I checked Signal's Privacy Policy and there are no details data sharing [1].

Signal might be good at message encryption, but let's not forget that it handles user privacy unacceptably poorly.

[0] https://github.com/signalapp/Signal-Desktop/issues/6002

[1] https://signal.org/legal/