Instead of linking to source code examples, which is easily misunderstood, here is Matthew Green's summary:
https://blog.cryptographyengineering.com/2020/07/10/a-few-th...
Alternatively, you can just open the app settings, which tells you that it will attempt to restore your contacts if you create a PIN:
> PINs keep information stored with Signal encrypted so only you can access it. Your profile, settings, and contacts will restore when you reinstall. You won’t need your PIN to open the app
If you want to go on believing that someone at Signal has found a way to backup your contacts so that you can recover them when you use a new device that does not in any way involve Signal collecting your contacts and storing that data to push back down to you later be my guest. You believe in magic, and I'll continue to believe their own statements, code, and documentation.
I've asked for evidence twice and you have supplied none.