Now THIS is new: Cloned SSD does not boot – a new twist

Pentagon, installed large disk (m.2, but with PCIe adapter) on PCIe. System boots, either with the old drive in the m.2 slot or not.
Either configuration allows access to all files.
With large disk in m.2,, whether or not the small disk is in PCIe, BSOD without capability to go into any of the recovery options.
Also, using either disk on PCIe will boot even though BIOS does not recognize either disk.

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Pentagon,
small disk is m.2 slot, BIOS recognizes it, but boot is from large drive on PCIe adaptor according to diskmgmt. Very strange.

captainron said:

With large disk in m.2,, whether or not the small disk is in PCIe, BSOD without capability to go into any of the recovery options.
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Pentagon,
small disk is m.2 slot, BIOS recognizes it, but boot is from large drive on PCIe adaptor according to diskmgmt. Very strange.

It is not strange, because you have to select the bootmanager from the bootoptions in BIOS!

In post #1
• Error code: Kernel security check failure. After three unsuccessful boot attempts get into Win rescue environment: Troubleshoot - Advanced Options – Startup repair – back to Kernel security loop.

In my interpretation it means that you have access to the recovery.
Only if you have access to command prompt, it makes sense to try suggestion from my reply in post #9

The frustrating thing is that with the old drive in m.2, the BIOS under Advanced Options shows the (old) drive with all the details. The big drive on PCIe is nowhere to be found in the BIOS, i.e. no choice given.
If I remove the old drive, i.e. m.2 is now empty and the big drive is on PCIe, the BIOS shows zero drives, yet boots.
Next setup: big drive in m.2, BIOS shows it with all details, but does not show anything for PCIe (which now has the old drive) (and, of course, does not boot).

The problem with Acer is, that they don't give proper manuals with details.
I am afraid that you have to use a Sata SSD for data storage. If the MB has SATA ports.
The partition layout of your old Kingston disk looks good.

Pentagon,
Thank you very much for your support - much appreciated. In the end I may have to live with the big drive on PCIe, and the original drive on m.2
Not ideal, but liveable.
Many thanks again, Pentagon!