2019 iMac: Sequoia on external SSD

I have a 2019 iMac 27”. Over the past couple of years, it’s been very slow, especially when rebooting. I did some research and learnt that this is due to the Fusion Drive.

So, I purchased a Crucial X9 Pro SSD, installed Sequoia on it, and migrated all my files from the old Fusion Drive. I also set up the SSD as the new startup disk. To be on the safe side, I decided not to erase the old internal drive just yet.

The SSD worked great for 2 months. Everything was loading fast, much smoother in comparison to the Fusion Drive.

Then, two days ago, I went to use my computer and entered the password for the user profile on the SSD. It wasn’t taking the password… I tried entering the password for the old Fusion Drive and it worked. This means that the computer went back to using the old profile on the Fusion Drive.

Now, the SSD is still connected (yes, I checked to make sure it’s plugged in correctly and also rebooted) but my computer is not seeing the SSD anymore. All I can see is this info in Disk Utility:

The SSD died already? In a matter of two months?!

I do not worry about losing any files because luckily I haven’t made many changes over the past few months. Plus, I always use Time Machine and have backups.

What I don’t understand is what happened to the SSD? I spent close to $200 on a solution that only worked for a very short period of time…

[Edited by Moderator]