Samsung Electronics GmbH
Hello,
Thank you for your enquiry.
The Samsung 970 EVO Plus NVMe™ M.2 SSD MZ-V7S1T0BW is not compatible with the iMac Retina 4K, 21,5, 2017 (iMac18,2). We recommend the Samsung 870 QVO, 870 EVO, 860 PRO as an alternative. If in doubt, please enquire directly with Apple support.
Kind regards from Schwalbach
Your Samsung Service Team

No.

It seems like apple uses some special kind of "Blade SSD" for these devices which have the slot notch in a different location. ifixit sells a compatible one on their website https://eustore.ifixit.com/products...

But from looking at the SSD replacement guides, it is far from a trivial process. The most difficult part being the part about removing the glued screen. If you are up for it though, ifixit has a written guide: https://www.ifixit.com/Guide...

and here is a video guide:
https://www.youtube.com/watch