need to recovevr data from my SSD - 256 GB - Late 2016 / 2017 A1708 13" MacBook Pro (656-0044A)

This comprehensive article on the subject describes the removable SSD used in your Macbook Pro but the conclusion is not encouraging.

https://beetstech.com/blog/apple-proprietary-ssd-ultimate-guide-to-specs-and-upgrades

OWC sells an SSD upgrade kit for the A1708 that includes a "transfer" drive enclosure for an SSD upgrade. I can't tell from the advert but you can call their tech lines and ask if that would work, and if it is available independent of the Kit:

https://eshop.macsales.com/item/OWC/S3DAP4NT02K1/

There doesn’t appear to be any external enclosure for that particular SSD. Possibly the only way might be to find a “donor” Mac. There are some answers in this previous topic.

Macbook pro a1708 fried--external hard dr… - Apple Community

Allan Jones wrote:

OWC sells an SSD upgrade kit for the A1708 that includes a "transfer" drive enclosure for an SSD upgrade. I can't tell from the advert but you can call their tech lines and ask if that would work, and if it is available independent of the Kit:

From the product page you linked (I highlighted the kit includes an external hard drive):

* On the included 1.0TB OWC Express external hard drive, create a Time Machine backup of your OS and files

So the OWC upgrade kit won't help the OP at all unless they can get the laptop to boot into macOS from either the internal SSD or from an external macOS boot drive.

I'm actually concerned that the OP's original SSD is failing which is very common with the 2016 & 2017 MBPro non-touchbar model. Assuming no accidental liquid damage, my money is on a bad SSD.

Assuming the SSD is healthy @y_p_w is correct.

In the future, I highly recommend having frequent & regular backups of your computer and all external media (including the cloud). There are a lot more new ways to lose access to your data on the USB-C model Macs. In addition it is impossible to recover accidentally deleted from an SSD after the Trash has been empties, plus an SSD can fail at any time without any warning signs (even a brand new SSD).

This Mac won't BOOT?

or this Mac won't even power on?

do you have another Mac?

Good point. I knew is was a long shot. Other OWC transfer enclosures are bare so you can put the old drive in the enclosure.

Looks like the end of the line.