Clean Install while existing merged partitions

I agree with @NavyLCDR. The OP should be " able to connect and read the second drive in order to retrieve any data from either one of those two drives." But how is a million dollar question which I wouldn't venture to answer or undertake.

To me it appears that the OP had the OS installed on a dynamic disk. Who did it and how? Only the person who did it can answer the question.

Dynamic Disk: Is it a simple volume? spanned volume? striped volume? Mirrored volume? What Is Dynamic Disk | Everything About Windows Dynamic Disk - EaseUS

Because of the complexities involved I will never venture into data recovery of dynamic disks. When the user meddles with the partition structure not knowing anything about the partition structures in a dynamic disk it becomes all the more complex. You are literally inside an infinitely long dark tunnel.

My advice to the OP: 1. Mark the two 6TB WD disks A and B and also mark the SATA slots to which those are connected.

2. Disconnect both the drives. ( When reconnecting, those should be connected to the same SATA slots)

3. Plug in the SSD to any other sata slot and reintall the OS. ( I would seek the advice of other experts whether this should be OK)

The aim is to make the OS boot cutting off the present linkage with one of those 6TB WD drives.

Once it is done, reconnect the 6TB drives A and B to the respective slots from which those were unplugged.

If the dynamic disks are simple or mirrored, the OP can use Partition Wizard Pro and use Method 1 detailed here Recover Files From Dynamic Disk In Windows, The Definitive Guide

• You can’t use “Convert Dynamic Disk to Basic” function to convert a dynamic disk containing other types of volumes except for simple volume and mirrored volume.

If it is striped or spanned volume - I don't know. You may turn to professional data recovery service.

Moral of the story: If you don't know a thing of what you are doing, don't do it.

I am not putting my hands into this because I don't know.