You can't make an anonymous Signal account, it is one of the biggest red flags that Signal has. You need a phone number.

Virtualbox would allow you to forward the webcam device to the webcam so you can use it as a regular camera on your virtual android. You then just need to figure out how to scan the qr code. If you search deeply enough, you will find ways to. Make android use an image or video as the camera source.

Just use android on Linux: waydroid

The anonymous part will depend on how you get your sms verification.

signal-cli software can do this without physical phone. https://github.com/AsamK/signal-cli/wiki/Linking-other-devices-(Provisioning)