I had the same problem installing update on 3 DELL Vostro i5 computers Windows 10 x64 Pro (the same configuration o those 3 computers, delivered the same day from the distributor on December 2019).
The problem first took place on July 2020 when trying to update 1909 to 2004, windows was installing and after reboot rollbacking the chenges to 1909.
On July 2021 windows was trying to install 20H2, also with error (0x80070020 or 0x80242016 or 0x1900101) on these 3 computers.
I have tried all the ways found on this MS forum and on others forums, even I had 3 talks with Dell consultants, and 2 technical Microsoft chats with
(one with remote desktop access to one of these computers). No one was able to help, the final answer was : download Dell ISO Windows 10 x64 Pro
and install windows againg (with data backup done first).
I have checked the update logs, analized the dump filed with the MS debuger installed from MS Store.
After many hours of looking I found one forum with the same problem, when the SSD drive was cloned and the update 1909 was not able to install 2004.
As I had the same 3 computers I was sure that Dell made one clean Windows 10 install with all the Dell drivers on one computer and then made SSD clones.
The solution was to check the BCD file (Boot Configuration Data) in the section {bootmgr} if there is missing device parameter :
- open CMD as Administrator
- bcdedit On these 3 Dell computers I had no device parameter in {bootmgr}, so next on this CMD I ran 2 lines, each after each (the C: drive is the Windows 10 drive)
- bcdedit /export C:\BCD.bak
- bcdedit /set {bootmgr} device partition=C:
Then close CMD, restart Windows, and after logging run the windows update. Then when windows installed the update and after rebooting there was 20H2
version installed !!!
Other people had also problems with BCD, but they had device parameter, they had some additional information that had to be deleted
bcdedit /delete {ID}
for example
bcdedit /delete {b2d1a263-cc33-11e9-a476-ec8e4d5eb847}
where {ID} was bad additional information.