Windows 10: Upgrade this PC now or Create Media for another PC?

bobkn might be on to something there, your machine booted, so the SysRes partition is ok. That leaves a possible issue with space.

I'd like to see your Disk Management.
Download this zip file (contains dmDskmgr-vd.mmc)

dmDskmgr-vd.zip

Striken: you can launch the MMC from inside the compressed folder.

Extract the mmc file (dbl click the zip to open, then extract all)
then dbl click the decompressed mmc file to run it

Double click dmDskmgr-vd.zip to open the folder
Double click dmDskmgr-vd.mmc to launch the custom Disk Management console
You'll get an output similar to this:

Press Alt+PrtScn to grab a snapshot of just that window
Open Paint and Ctrl+V to paste it, then save the image
Attach the image to a new post.

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I helped members during the Preview do exactly what the link bobkn pointed to suggests. I grew the part to 450 MB, but it seems as though a Win10 Clean install creates a SysRes of 500 MB (drat ... I was so close)
I even started building a thread. I'll see if I can find the pieces (I never posted it) - it even has pretty pictures
It is fairly simple, one set of commands does it all in Minitool Partition Wizard.

I'll look for my grow the System Reserve partition instructs, while you collect and post the disk management information on your machine.