Good to know! Thanks.

I notice the README file for signal-cli [1] says registration "may require solving a CAPTCHA challenge", which might involve running proprietary software. I found a forum post that says this also sometimes happens on sign-in [2], which might make it difficult to use Signal without proprietary software. I might try it anyway at some point because it does say "may" :)

[1] https://github.com/AsamK/signal-cli [2] https://community.e.foundation/t/signal-and-hcaptcha/83470