Premise: I did this in an external SSD drive system.
I followed the tutorial, added new clusters to the disk in Disk Utility (current system, external ssd, current external ssd), then registered the device at: https://beta.apple.com/zh-CN/enroll-your-devices, downloaded the beta system in Settings, and then clicked on Upgrade, and it didn't come up to let me choose which zoned volume to install to, directly the system automatically rebooted multiple times and upgraded the current system to beta.
Question 1: Why is there no disk selection? Is it an external ssd system where selection is not possible?
Q2: Can I downgrade back to the original system now? Can I downgrade back to my original system now and do it all over again?
QUESTION THREE: How do I correctly install beta in the new dossier instead of the current system.