>5. ISTR you said your machine has an OEM Samsung SSD of some kind. I would look hard for a diagnostic for its particular model. Failing that, many name-brand computer builders such as Dell and HP have built-in diagnostics which can test the disk (amongst other things) regardless of make/model of that disk

I have installed HP PC Hardware Diagnostics.

The first test wasn't very appealing. See image 1.

Then, I wasn't able to click Finish. I had to click on the X. This disabled the image on the HP PC Hardware Diagnostics desktop icon. When I clicked on it again, it says "Only HP Devices Are Supported".