You get a unique phone number, signal sends the activation text, you confirm the account. And they add the number to a blocklist so no one else can use that number and screw your account up. I’ve done it for Discord, Telegram & Signal. I have Signal running in Waydroid right now, without my phone number attached to it
I don’t think you can use another number that isn’t the phone number tied to your device when you use Signal mobile app.
I have two phones and Signal refused to let ne sign in on phone a using phones b’s number.
This isn’t the site I normally use, but it’s another one:
https://grizzlysms.com/signal
You get a unique phone number, signal sends the activation text, you confirm the account. And they add the number to a blocklist so no one else can use that number and screw your account up. I’ve done it for Discord, Telegram & Signal. I have Signal running in Waydroid right now, without my phone number attached to it