No disc to download Monterey

You need to back out of the installer and open Disk Utility.

Select "Show all devices" from the View popup menu.

You should see a device named something like Apple SSD 256GB...

Are there any containers or volumes indented below it?

If not, select the drive device and Erase. Create an APFS formatted volume with GUID partition map. Name it whatever you want. When you go to Install, you should see that volume as available for the installation.

If you do see other things indented, please post a screenshot of that. Use the image button in the toolbar to post the screenshot.

One does not Accidentally Delete everything on an Apple Computer.

One may do this without the Knowledge of what the outcome may be.

Was this method from Apple Specific to Apple Silicon Computers used --- >>

Use Disk Utility to erase a Mac with Apple silicon

Then this Apple Method specific to Apple Silicon Computer

Use macOS Recovery on a Mac with Apple silicon - Apple Support (CA)

It would help to know the hardware as intel and Apple silicon are quite different, however if you can get to the Monterey installer on the device, hunt around on the menu bar and launch disk utilities from the restore partition, if you don’t see and can’t repair to the state of having on APFS volume group, then erase the drive at suto root level and set for APFS, not encrypted, not case sensitive. Just make a single volume, that’s all the installer needs to make the many companion containers and volumes and install onto them. The first time you log in, go to “system preferences” click “security and privacy” then “FileVault” and encrypt your drive. It’s unusual to damage a drive in a way that this won’t recreate it, albeit without your data.

hopefully you have backups or don’t have anything important on the drive. If you don’t have backups and do have prized data do not erase the drive. Just use first aid in disk utilities and if it doesn’t work, launch the machine in FireWire drive on an intel machine, or share disc on Apple silicon and use disk utilities externally and or other recovery tools, disk drill being the simplest.

if you have two computers or can barrow another and none are super old, installing Apple configurator on the other computer then reviving or restoring your computer with it is bulletproof and the only method I know of to fix an Apple silicon computer with damage to the lower 3 levels of the internal drive because that’s where the firmware and recovery and preboot volumes are.

good luck