Did you test the performance?

Marcel: Would be nice to know what the performance is like.

Which adapter exactly did you use?

Is the Samsung EVO 970 M.2 NVMe slower than the (more expensive) OWC SSD due to the adapter?

As mentioned above, you need MacOS 10.13 High Sierra (or later).

Normally you would install that first, then install the new SSD.

Have you tried booting from USB on a newer version of MacOS and installing that way?

Just installed on a MacBookAir6,2 (13-inch, Early 2014).

Was very easy.

New iFixit battery looks great so far:

Full Charge Capacity (mAh): 4922 -> 7333