bricked 2014 iMac

AFAIK, the Apple Configurator 2 is only meant to resolve firmware issues with the USB-C Macs and not older Macs.

Try a PRAM Reset (hold the PRAM Reset for at least three chimes).

See if you can boot the Apple Diagnostics to see if any hardware issues are detected.

If you cannot boot the Apple Diagnostics, then try Option Booting the iMac to see if the Apple boot picker menu is displayed (even if it is empty because the hard drive has failed or no longer contains a bootable OS). If you can at least access the Option Boot menu, then there is hope on reviving the iMac. Otherwise the Monterey upgrade may have corrupted the system firmware. Unfortunately I'm not aware of any way to reinstall the firmware except to have the Logic Board replaced (very expensive) or to have someone replace the firmware chip (non-Apple unauthorized repair). Years ago Apple used to provide images so users could create a firmware restore CD to fix firmware that was corrupted during an OS upgrade, but Apple has not done this since before 2012.

If you are unable to Option Boot the iMac to see the boot picker menu (even if no bootable volumes seen) or boot from external media (Apple Diagnostics, Internet Recovery Mode), then the firmware may have become corrupt during the upgrade. The diagnostics and Internet Recovery Mode don't need to fully boot, they just need to start the process which means the iMac in not "bricked" by corrupt firmware. The Big Sur upgrade installer last year was confirmed to have corrupted the firmware on 2014 MBPros (the T2 Macs which had corrupted firmware usually were able to "Revive" or "Restore" the firmware using Apple Configurator 2) and Catalina also had some issues as well (I cannot find the articles with more details at the moment -- Apple actually blocked Big Sur for a while for those with 2013 & 2014 MBPros last year).

https://9to5mac.com/2019/10/24/efi-firmware/

https://eshop.macsales.com/blog/67909-big-sur-problems-macbook-pro/

https://arstechnica.com/gadgets/2021/11/why-macos-updates-might-brick-your-mac-and-what-you-can-do-about-it/

https://arstechnica.com/gadgets/2021/11/apple-fixes-bug-that-caused-macos-monterey-update-to-brick-some-apple-t2-macs/

If the iMac doesn't have corrupt firmware, then the hard drive may have failed since an OS upgrade can stress an old drive. The Apple Diagnostic can detect some drive failures. However, a more reliable way of detecting drive failures when macOS won't boot normally is to create bootable Linux USB stick which has a utility to check the health of hard drives & SSDs. I can provide instructions if you are interested, but you will need access to another computer in order to create the bootable USB stick.

Sometimes you just need someone who can actually see the computer first hand in order to make a proper diagnosis.

What happens when you Option Boot the iMac? Do you see the boot picker menu (even if there are no bootable items listed)? The important thing is seeing the boot picker menu which tells us that it may be possible to boot from a USB drive. If the boot picker menu is visible, then it may be possible to boot a Linux USB stick since Linux is a bit more forgiving when booting even if the hardware has a problem. Sometimes a bad hard drive can prevent a Mac from booting from any external media and may prevent any external boot volumes from showing up on the Apple boot picker menu because the errors of a failing drive cause the search for bootable volumes to time out (although I believe you may see a spinning wheel/gear). I would hope for a failing drive, but the only way to see if that is the case is either by disconnecting the internal drive which is not easy to do on an iMac or by being able to boot from a USB stick (not always possible).

You can create a bootable Knoppix USB stick by using the downloaded Knoppix .iso file as a source for Etcher (Mac/Windows/Linux). Use the Knoppix v9.x DVD with "EN" in the name for "ENglish". Option Boot the Knoppix USB stick and select the orange icon labeled "EFI". The Mac may appear to be frozen on the boot picker menu while Knoppix is booting so give Knoppix lots of time to finish booting.

I'm currently working on a laptop that may have had a failed Big Sur upgrade (unfortunately I'm not certain if the laptop had an issue before the upgrade attempt or if the current issues are the result of a failed upgrade). It is very hard to boot to any external media, but I did find a way to do it. The diagnostics did report a corrupted firmware and I'm unable to perform a PRAM Reset. Unfortunately updating the BootROM firmware did not fix the boot issue or PRAM Reset issue. It is possible there is another firmware that is actually corrupt (SMC?) which makes sense due to my work around for booting external media (I forgot to check the SMC version before the upgrade). Haven't had time to see if the diagnostics are still reporting a firmware issue, plus I still want to eliminate the internal drive as contributing. Just mentioning this since it may not be a straight forward easy to figure out answer for your iMac either.

Please try booting the computer while holding down the power. Button for about 15 seconds and let us know what happens.

Please re ask your question with much more information. Please remember we do not see what you do and cannot look over your shoulder so we rely on you to write a descriptive question so we can get a good idea what is happening. I'd recommend first reading Writing an effective Apple Support Communities Question

Is there a reason you have not taken it in for service. My guess is you have a hardware issue and it is not software.

However, by chance do you have an third party antivirus, cleaning or any other third party maintenance apps installed ?

I think it is either going to have to be serviced and I know that will be challenge with your condition. While a 2014 is not ancient by any means it is also not beyond the realm of thought of possibly replacing it. Is that something you are open to? To be honest if I were in your shoes I think I might consider a Mac Mini.