I backed it up using time machine before upgrading, but it is totally unresponsive (no screen, power button does nothing). I have a 2020 Macbook Pro if that is helpful. Does anyone have any suggestions on what to do?
Unfortunately the Macbook 12" is not an Apple Silicon device, nor is it a T2-based Intel Mac as far as I can tell.I found this in my archives -- it might be of use (even though you don't have a t2 Mac, but Apple Silicon instead):
How to Restore BridgeOS on a T2 Mac + Boot a Mac to DFU Mode
macOS Update brick your Mac? This article will show you how boot to DFU Mode and restore BridgeOS on a T2 MacBook Pro, Air, iMac Pro, Mac Mini & Mac Pro!mrmacintosh.com
Also, look at this:
Thanks. Unfortunately this wasn't helpful.
Use macOS Recovery on an Intel-based Mac
Learn how to use macOS Recovery on an Intel-based Mac.support.apple.com
Start up your Intel-based Mac in macOS Recovery
- Restart your Mac.
- Immediately press and hold one of the following key combinations until you see the startup screen:
- Command-R: Start up from the built-in macOS Recovery System. Use this key combination to reinstall the latest macOS that was installed on your system, or to use the other apps in macOS Recovery.
- Option-Command-R: Start up from macOS Recovery over the internet. Use this key combination to reinstall macOS and upgrade to the latest version of macOS that’s compatible with your Mac.
- Option-Shift-Command-R: Start up from macOS Recovery over the internet. Use this key combination to reinstall the version of macOS that came with your Mac or the closest version that’s still available.
- If you see a lock, enter the password for your Mac.
- If you have multiple volumes on your disk, select the volume you want to recover, then click Next.
- If requested, choose an administrator account, click Next, enter the password for the account, then click Continue.
When the Recovery app appears in the menu bar, you can choose any of the available options in the window or the menu bar.