Can you boot macOS normally?
If so, then create & use a bootable macOS USB installer using the instructions in the following Apple article:
Create a bootable installer for macOS - Apple Support
If not, then do you have access to another Mac from 2007 to 2020? If so, then you can use that other Mac to create a bootable macOS USB installer using the following guidelines:
- macOS 11.x Big Sur installer generally needs a Mac from Late-2013 to 2020
- macOS 10.15 Catalina generally needs a Mac from 2012 to 2019
- macOS 10.13 High Sierra generally needs a Mac from Late-2009 to mid-2018
- macOS 10.11 El Capitan generally needs a Mac from 2007 to 2015
You can confirm the other Mac is compatible with the version of macOS by using the information in the following article (the other Mac can currently be running any version of macOS 10.6+):
https://eshop.macsales.com/guides/Mac_OS_X_Compatibility
Otherwise try booting into Internet Recovery Mode using Command + Option + R to attempt to access the online macOS 11.x Big Sur installer. Unfortunately some Macs will only boot to the online installer for the older version of macOS which originally shipped with the Mac from the factory....while that should be Ok, some people have had issues with the older online installers.
No matter which option you use, there is no need to authenticate when reinstalling macOS even if Filevault is enabled on the internal SSD. When you boot to the macOS installer, launch Disk Utility and erase the whole physical internal SSD as GUID partition and APFS top option (for macOS 10.15 or 11.x). Otherwise you will need to erase the whole physical SSD as GUID partition and MacOS Extended (Journaled) for macOS 10.11 or 10.13. Within Disk Utility (for the macOS 10.13+ installer), you will need to click "View" and select "Show All Devices" before the physical drive appears on the left pane of Disk Utility. After properly erasing the internal SSD, close Disk Utility and select "Install macOS" (or it may be "Reinstall macOS").
