Same Problem here with ASUS N56VZ Notebook (2012)...
After many attempts to solve the 0xc1900101 error, I figured out there were too many entries in the BCD (Boot Configuration Data) orphaned and the redirection-entries linked to deleted partitions ..
Solution is to delete the orphaned entries:
To show the BCD entries:
1) Start command prompt: hit start, type in "cmd" and by pressing shift+ctrl press enter to start cmd-prompt with admin-rights
- Type "bcdedit /enum all" in the opened command-prompt window and press enter. Now you get a list with all entries of the BCD Data, one named "Windows Boot Manager" and two "Windows Boot Loader" entries.
On my N56VZ Notebook there were 5 entries named "Windows Boot Loader". I had to delete 3 of them to get the 2020h2 update running.
To find out the wrong "Windows Boot Loader"-entries:
1) find the string after "resumeobject" in the list of the "Windows Boot Manager". (i.e. {f769421f-c665-11ea-9d4b-a58aceca50cd} )
2) Search this string in the "Windows Boot Loader" entries under "resumeobject". The entry beginning with that number and the other with the string "{current}" are the right ones.
3) Delete the other (orphaned) entries of "Windows Boot Loader" (orphaned entries show under "device" some "?"-Symbols ) with the tool "Visual BCD", simply search for it.
After that procedere, Windows Update was able to run the full update to Win 10 2004 :)