Mac Mini mid 2012 best way to backup system for new Hybrid SSD

If your Mini does not have the two "dimples" on the bottom cover, then you have a 2014 model since the older models have two "dimples" on the bottom cover to aid in rotating the cover to remove it. A 2014 Mini which had an SSD installed from the factory has a flex cable for a blade style PCIe Apple SSD. You can get the exact model of the Mac by clicking the Apple menu and selecting "About This Mac".

If you have the 2014 Mini with a Fusion Drive setup, then trying to clone or migrate will be a complex chore since you cannot remove either of the internal drives or you will destroy the Fusion Drive with your data. You also cannot connect an OWC NVMe SSD externally since there are no enclosures available for that OWC NVMe SSD. Even OWC does not have a compatible enclosure for their own NVMe SSD. This means you would need an external USB3 drive to clone your Fusion Drive to it, then install the OWC NVMe SSD, then clone the external drive back to the internal drive.

To use an NVMe SSD, you will need to first have macOS 10.13+ installed so that the system firmware has been updated to work with an NVMe SSD and you will only be able to use macOS 10.13+ with the NVMe SSD.

If you have a 2012 or earlier model, then the OWC Aura NVMe blade style SSD will not be compatible as the 2012 and earlier models only support 2.5" SATA drives.

I use Carbon Copy Cloner to clone drives before swapping. I put the new drive in an external transfer enclosure (cheap USB3 enclosure) where I format it using Disk Utility, Only then do I do the cloning. Then I install the new drive n the computer.

I use CCC because it prompts you to create the important recovery partition on the old drive to the new one. Get CCC only from the developer's site: https://bombich.com

You are making it far too complicated.

Just replace the 2012 Mac Mini's HDD with a large 2.5" SATA SSD.

https://eshop.macsales.com/shop/ssd/owc/mac-mini/2012

FWIW you can use most any 1, 2 or 4 GB 2.5" SATA lll 6G SSD in the 2012 Mac Mini.

(Crucial, PNY, WD, OWC, etc..)

Then you can simply have macOS and your data on the one SSD and easily back up to an external drive.

What are you going to plug the PCIe drive into?

The 2012 Mac Mini only has internal SATA lll 6G internal connections on the logic board and 4 external USB 3.0 ports.