Late-2015 iMac 27" can't see Crucial X6 2TB drive

I have a late-2015 iMac 27" with a wonky fusion drive and want to attach an SSD and boot off that. I bought a Crucial X6 2TB drive(has USB-C to USB-C AND a USB-C to USB-A adapter). I plugged it into Monterey on the iMac, but it doesn't recognize it. Nothing is coming up in Disk Utility. Rebooted, still nothing visible. I took it to my 2019 MacBook Pro and it could see it using the USB-C to USB-A adapter. So I erased the ex-FAT partition and set it to APFS and took it to the iMac. Still doesn't recognize it. Tried multiple USB 3 ports. Nothing. Anyone have any ideas why? The drive is good, the cable is good. I just can't see it on a newly installed Monterey OS on the late-2015...any ideas would be greatly appreciated.