MacBook-pro Internal PCIe Samsung 512g SSD no longer recognized on MBP (mid 2015 15" A1398) after crash and hard reset

The 15" MBP Retina Mid 2015 MacBookPro11,4 (A1398) is at most 5 years old. All drives fail, it is merely a matter of when. You have learned a valuable lesson about backups. It is interesting that Recovery Mode boots from the internal SSD or is that from an external drive? I suspect the latter but your description jumps around so much it's hard to tell.

While booted from an external drive if you open Terminal and run the diskutil list command do you see the internal physical drive /dev/disk0 listed with the EFI, Apple_Boot, Recovery? If not, then the drive is definitely not being seen at all. You could try booting from various macOS installer versions (Yosemite, High Sierra, Mojave, Catalina) on a flash thumb drive and run the Terminal and the diskutil list command on each. As the file systems vary from JHFS+ to APFS.

At this point you should probably just replace the internal SSD with a new SSD which fortunately is possible on this model of MacBook Pro. Newer MacBook Pros have the SSD soldered to the system board but not your model.

If you cannot see the drive at all is a clear indicator that the SSD has completely failed. If after replacing the SSD you cannot see the new drive then the system board has a failure. If it was merely a messed up core storage conversion to APFS or other soft failure of the data organization on the disk, it would still show up as a drive. It would appear even if nothing was on the drive.

You can send the SSD out to a data recovery company to take a crack at recovering data but it can be very expensive. It may require removing the flash chips and placing them in a special rig using very specialized software to read every sector bypassing the drives firmware. Then more software to decode various layers of core storage and JHFS+ or APFS formatting. Even then you might receive back a jumbled mess of partial data. The more effort involved in recovery the more it costs. When SSDs fail there is often no warning unlike mechanical HDD drives which make noises, report failures, etc.

But sadly, you will not find any magic bullet software to fix/repair a drive that is not being detected. At that point, your options require significant tooling and skill to access the flash chips directly. If it was encrypted you need to supply the recovery key to the data recovery specialists.