Triggered the update from System settings, the phone rebooted, and now it only boots into Fastboot. System is unusable.
Vendor Name: Xiaomi
Device name: Redmi Note 8T
Device CodeName: ginkgo/willow
Version of /e/OS or Stock which existed previously: 1.21
Is the device Rooted: no
EDIT: I was able to restore the system to the previous version by dirty flashing the 1.21 recovery, then wiping cache, finally flashing 1.21 from recovery, and then resetting network settings once booted into the system to make WiFi work again. At least the phone is usable again, but this was a one hour command line enterprise and far from something a non-technical user would be able to solve, and I’m still on the old version.