Cumulative update December 2020 - KB4592438 Failed to install

None of the methods above worked. But I tried the update tool link and at first it failed and I got a blue screen then I tried one more time and now all is working and all of my programs and files were not modified.

I am trying to install KB4592438 for Windows 10 20H2. The patch is downloaded without any issue. But the installation fails and the screen starts showing - Undoing changes Don't turn off your computer. The error message is - Some update files are missing or have problems. We'll try to download the update again later. Error code: (0x80070003). 

Okay thank you for allowing me to present my problem here.     So I tried turning off the Firewall. I tried downloading that small app that changes the update folder, I used the Partition Wizard to add 20 gigs from the C drive to each of the other drives.   Still no luck on installing the the "kb...438" update.   It seems that my "System Reserved" partition is not visible on the Disk Management.   The info I found online seems to suggest that if it was accidentally deleted that my computer would not boot which of course is not the case.      Would a factory wipe deal with all of this?    If it is an issue of being out of space in some way that I cannot see, wouldn't starting over lead me to the exact same place by the time my laptop gets to the 438 update?     Hopefully I am not being too convoluted here.  Thank you so much for any advice!

This is the only thing that worked for me.  THank you!