I've released instructions for anyone who is having this issue. ?
You are affected by this issue if your T2 Intel Mac (2018-2020) is booting up to a black screen after installing the Monterey 12.0.1, Big Sur 11.6.1 or Catalina 2021-007 Security Update.
You will need a 2nd Mac for the fix and will be restoring the BridgeOS firmware. Once connected, you will perform a REVIVE. This will fix the issue + retain all OS and User data.
The Apple Store can do this for you but BE SURE to say you need a REVIVE and not a restore. If they click the restore option all your data will be ERASED.
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