How to resolve Issue with SSD with Folder with Question Mark Issue?
In this model the SSD 'stick' slots into a rised slot on the motherboard, there is no cable. So given that the SSD is not detected at all in Recovery mode, my take is that it is hardware: either the SSD itself or the motherboard power circuitry to the SSD slot. The only sure way that I know of to differientiate between the two possibilities is to open the Mac, remove the SSD (which is fairly simple, just one T5 screw), and put the SSD into either an existing MacBook Pro/Air (any of the two, years 2013-2015 will work) or an external adapter of the kind you mention and see if it works.
Note that a USB adapter will have to be specifically for 2013-2015 MacBook Pro/Air SSDs to fit the SSD you have.