Here are some steps you might consider:
1. Since you're not concerned about data on the drives, please try to erase the faulty drive with Disk Utility.
2. Boot into Recovery Mode and use Disk Utility to see if you can format the SSD.
3. Sometimes resetting the Non-Volatile Random-Access Memory (NVRAM) and System Management Controller (SMC) can resolve boot-related issues. Follow Apple's instructions for your specific iMac model.
4. Try reinstalling macOS on your SSD. Make sure you format it correctly during the installation process.
5. Ensure that your iMac is set to boot from the correct drive after macOS installation. You may need to adjust startup disk settings in Recovery Mode or via the Startup Manager.
6. If the above steps don't resolve the problem, you might need to consult with an Apple Authorized Service or Apple Support directly. They can diagnose some hardware problems.
You can also refer to Fusion Drive Not Showing Up or Not Working on Mac? Fixed!