I installed macOS Sequoia Beta 1 on external SSD and I boot it on my MacBook Pro. I changed my startup disk in Settings to point SSD and I install update via "Software Update". The file is downloaded then my computer restarts and it takes around ~20 seconds to install everything, but once the macOS is started, I see that I've got still Beta 1.
I tried also to download the full installer and repeat the process but with the same result.
It looks like everything is installed correctly, but once the system is launched, it's still the old macOS version.
Any idea how to update the system on my SSD?