Fresh install of aurora, running system update bricks my installation

I’m trying to run Aurora Surface on my Surface Pro 9.
I disabled secure boot, disabled secure core, used Ventoy to load the ISO, and I installed the OS on an external hard disk.
I managed to boot into the system, then did a system update. It appears to have resolved without problems and prompted me to reboot so I did.
However when I try to boot into the new OS, it just gets stuck at the windows + aurora logo with the spinner stuck.
I can boot into the original configuration at least, so if there are any logs I should supply, let me know!

EDIT: actually, the boot screen shows up for too short a time so i can’t select the older version reliably, if there are any tips for that, that’ll be welcome.