As stated in this [1] datasheet from WD, it is backwards compatible with PCIe gen 2.
[1]
https://documents.westerndigital.com/content/dam/doc-library/en_us/assets/public/western-digital/product/internal-drives/wd-blue-nvme-ssd/product-brief-wd-blue-sn550-nvme-ssd.pdf
I was able to clone the disk. Acronis must be downloaded from the WD site and the disk must simply be connected so that it is recognised as WD. It can happen with adapters that the chip of the adapter is recognised instead of the disc. (I had this problem with a USB adapter).