Have you tried DFU Mode? This should fix your issue; however, start by doing a REVIVE, and if that doesn't work, do a RESTORE.
In order to do this, you need:
- Second Mac running Catalina 10.15.6 or later
- On that Mac, you must have a copy of Apple Configurator 2 (downloadable off the App Store)
- A USB-C or USB-A to USB-C cable that supports power and data transfer (Thunderbolt cables not supported)
- You CAN use the USB-C charge cable of a MacBook if you want
For instructions on how to do a restore using DFU Mode, here are the official instructions:
https://support.apple.com/guide/app...ore-a-mac-with-apple-silicon-apdd5f3c75ad/mac
You can also download a trusted version of macOS in an IPSW image, and then drop that into AC2 when you do the restore.
Obviously the problem with this is that you need a second Mac running 10.15.6 or later. So if you don't have a second Mac running that OS, you will have to somehow acquire one.
Hope this helps.