How to erase data only on 2015 iMac running Monterey?

What is the purpose for this erasure?

If you will be transferring ownership of this Mac, then this is the guidance you must follow to ensure the new owner can fully and freely use the device: What to do before you sell, give away, trade in, or recycle your Mac - Apple Support

This must be done to release the Mac from your Apple Account and Find My.

This will erase all non-Apple data, including third-party apps that don't come with the OS.

If you simply wish to wipe your old user data so that you can retain the Mac and start over, I like this:

• Create a new local user account with admin privileges and delete the old one.

Add a user or group on Mac - Apple Support

Delete a user or group on Mac - Apple Support

Oh! I do see that Apple have not included the Monterey OS in that linked document. That's surprising.

The guidance for Monterey is similar, if not identical, to that for those included macOS versions. The process has not really changed at all over many generations of OS.

Take a look at this one:

Set up users, guests, and groups on Mac - Apple Support

You’re welcome.

Happy to know you got this done. 👍🏽