Yes, the M.2 NVMe SSD in Netstor Thunderbolt 3 NA611TB3 / NA622TB3 storage can be used as the macOS boot disk for the Mac computer. The standard operating procedure for installing macOS on external Thunderbolt 3 M.2 NVMe SSD is as follows:

1. At macOS’s Disk Utility, format the external Thunderbolt 3 NVMe SSD as APFS format.
2. Go to macOS’s App Store. Key in macOS in the search bar, and press enter. Then you will see the macOS installer (free of charge) from the App Store. Click on the download button to download the macOS installer at App Store to your Mac computer.
3. After the downloading finishes, execute the macOS installer, select the SSD (the external Thunderbolt 3 NVMe SSD) as the target installation drive [see the image below], and click on Install button to continue with the macOS installation on the external NVMe SSD.
   
4. As the macOS installation on the external NVMe SSD completes, the Mac computer will boot into the macOS on the external Thunderbolt 3 NVMe SSD automatically. At this time, click on the Apple icon at the top left position of the screen, select About This Mac, and then you will see that the Startup Disk for the system now becomes SSD [the external NVMe SSD] meaning that at the present your system is currently booting with the macOS on the external Thunderbolt 3 NVMe SSD for work.