Hi,
One way to start trouble shooting is remove SSD and boot up with a Linux usb to see if laptop is functioning properly.
Then put SSD in an USB enclosure connect to laptop and see if you can mount it and read it with Linux.
If there’s no issue doing this then I would start looking at SSD cable on mainboard being possibly faulty.
The only way to check this would be substituting the flex cable and testing.
Hope this helps