Theoretically possible, but extremely risky since you can permanently split the Fusion Drive if both drives do not go ready at the same time. I've only seen one success story on this forum with dozens more stories of failure. If you don't have a backup, then I would highly recommend contacting a professional data recovery service.
The only safe option for you to try is see if you can put the iMac into Target Disk Mode and connect it to another Mac using a Thunderbolt cable. You do not need to see anything on the iMac's screen in order for this to work. Whether this will work depends on the actual hardware failure. Your other host Mac needs to be running macOS 10.13+ (maybe 10.12), but you still may need to manually mount the "Data" volume on the iMac and navigate to it with the Finder since that is where the user data resides on macOS 10.15+.