IMac Start Up & Missing HD

I’ve recently been experiencing startup issues with my iMac. It began with the iMac stalling about halfway through the progress bar before crashing. I believe this problem started after I upgraded to macOS Monterey.

I attempted to enter Recovery Mode to reinstall the operating system, but the process stalls around “13 minutes remaining” before crashing again with an error. I’ve also run First Aid on the drive, which often returns errors, although it has occasionally completed successfully. Despite these efforts, I still can’t get the iMac to boot properly.

To recover some important files, particularly photos, I purchased a Thunderbolt cable and adapter to use Target Disk Mode to transfer files to my MacBook Pro. Unfortunately, the iMac crashed during the transfer of my photo library, forcing me to reset it by holding the power button. Since that crash, the iMac’s “Macintosh HD” no longer appears in Disk Utility or Recovery Mode.

Since then, I’ve encountered several error messages during boot attempts, including the “question mark” folder and the “circle with a line through it.” When I do manage to enter Recovery Mode, it now only offers an option to install macOS El Capitan, but the installer cannot locate the Macintosh HD drive. Most attempts to boot end with an error message instructing me to contact Apple Support, with error code -2102F.

Is there any other way to fix this/recover some photos that were on the iMac ?

Any help would be greatly appreciated. 

Thanks