I thought that this was "Solved", because on the freshly-installed Dell 11.6" laptop I finally got it working on, Windows Update said "Up to date".
I just tried the same script on a Lenovo IdeaPad 100S, with possibly an older release of Windows 10 (Edit: No, it was 1903 Home 32-bit), that had pending updates "in the queue", and the script seemed to complete successfully, but when I went to update, it said that the four items that it was updating, all "Failed to download".
I tried deleting the \SDcard\SoftwareDistribution\Download directory, or clearing the contents, and trying again, and again, "Download error".
So I blew away the \SDcard\SoftwareDistribution folder entirely, deleted the \Windows\SoftwareDistribution link, let Windows Update re-create the \Windows\SoftwareDistribution folder, and am now updating the system (on the eMMC).
After that's done, I'm going to try it again.
Edit: I wonder if this has something to do with the SD card being listed as "Removable" in Disk Management. I did delete the exFat partition and re-format as NTFS, mounted in the \SDcard directory.
Edit: I tried deleting \SDcard\SoftwareDistribution entirely, as well as \Windows\SoftwareDistribution , after stopping the four services listed in the script, and then re-starting the services, rebooting, doing Windows Update (which should have re-created it), then running the script, which stops the four services, and then robocopies the \Windows\SoftwareDistribution directory to \SDcard\SoftwareDistribution (*including permissions, which is why it uses RoboCopy), and then blows away the \Windows\SoftwareDistribution directly, and replaces it with a "Junction" to \SDcard\SoftwareDistribution.
Interestingly, though, for some reason, on the laptop that this worked on, the "Junction" shows a blue arrow towards the top of the folder, and the "Junction" created with the same script, on the IdeaPad 100S running 1903 Home 32-bit, shows a "Link" on the lower-left corner of the icon, like a shortcut. (Edit: No, I'm incorrect, both systems had the "link" overlay icon on the bottom-left of the folder icon.)
Not sure why the appearance is different.
Also, I did mess with and download the now-obsolete (? now the mklink supports the '/J' option for Junction) junction.exe from sysinternals (2010), and used that on the Dell that this worked on, but I since deleted the "Junction", and used the above script to re-create it. I just wonder if using the "junction" tool, made some sort of less-than-visible change to the NTFS filesystem, or created a registry entry, and that's why the script worked on the Dell (1903 Home 64-bit), and not the IdeaPad 100S (1903 Home 32-bit).