Can you hide/disable the internal SDD blade in an iMac (originally Fusion)? The 128GB SSD internal to my mid 2015 iMac's original fusion drive setup died, and can not be acted upon by Disk Utility (can't mount, repair, etc). The original setup has already been split into two separate drives, so all files are on the larger internal. Unfortunately, the dead drive appears to periodically cause random reboots, with an error saying I shut down my computer because of a problem. How can I stop the computer from seeing this drive entirely?

Other information:
• I looked at a similar question here, but I can not reformat the drive as free space as recommended. Simply setting hard drives to sleep when possible did not work
• I don't believe I can use fstabs because I can't get a UUID from diskutil. Although, I have seen usage of the LABEL identifier in the fstabs file. Could this help?
• I'm currently running Catalina, but I might be open to others.
I'd suggest this a hardware problem: you'd be best served by finding a local independent Apple repair company, and asking them to replace the SSD with a new/secondhand Apple unit.  

They'd be experienced at taking it apart and would charge a reasonable price. An Apple Store might say it's too old, or charge a lot.

The same modules are used across Apple's hardware of a similar age, so you should be able to get a larger size -- 512; 1Tb. (Don't Fuse with the HDD!) 

If your OS is on the HDD, that's massively limiting the performance of your iMac.