Cumulative update KB5001330 fails to install

It should be no problem!
then you have installed an old program, because it is not a corporate computer where the group rules apply?

English. The standard is American English.

Yes I agree with you!
Good luck!

I can ask in which language you use Windows because it also matters?

Apparently, Microsoft has some concerns regarding 21H1. From their website: "We are throttling availability up over the coming weeks to ensure a reliable download experience for all, so the update may not be offered to you right away. Additionally, some devices might have a compatibility issue for which a safeguard hold is in place. In these cases, we will not offer the update until we are confident that you will have a good update experience."
It seems that they are currently rationing the general release. Since one description of 21H1 contains reference to Windows Defender, I am guessing that Defender updates are failing on my computer because I do not yet have 21H1. Given that I know virtually nothing about how Windows works, I will wait until they deem it proper to provide me with it.

I didn't use the ISO route. I use the Windows May 2021 Update route and it still failed. Also it took almost 2 hours only for all changes to be rolled back.

So I thought that the installation will fail!
That's why I don't encourage you to download ISO myself just because of the update!
For me the update lasted 1 minute because the computer had a full installation environment, windows update service asked if I installed 21H1 manually .> install and no problem !
Proposes to wait and do not rush!

I tried upgrading my Windows 10 Pro X64 20H2 to 2!H1 X64. Although I had downloaded the 21H1 Iso I took the Update route. Everything seems to go well until the Updating Windows process which at about 95% complete which I thought everything was going well. Then, the screen changed to black the message "Undoing changes made to your computer ". So back to square one. The whole process to nearly 2 1/2 hours of my time. So I never got my Windows upgraded to version 21H1.

An upgrade on my current build Windows just won't work for some reason. The only option for me now is to do a custom clean install of 21H1 on the same partition as my existing Windows which will later becomes Windows.old. Although I don't have to re-activate I will lose all my applications - my data is stored in a 2nd drive.

Wrote:

SOFTWARE ⋮ WINDOWS 10 UPDATE
Direct Download Windows 10 May 2021 Update v21H1 ISO Files (32-bit / 64-bit)
By Rafia Shaikh
May 18, 2021 13:39 EDT
download windows 10 21h1 iso windows 7 windows 10 iso 32-bit windows 10
Windows 10 May 2021 Update is live! After several months of Insider testing, the May 2021 Update, version 21H1, is going live for the public. Like the previous versions, this would be a phased-out rollout, meaning not everyone would get it at the same time. However, through the ISO files, you can force and clean install Windows 10 version 21H1 on your devices without waiting for the official availability.

Direct download Windows 10 21H1 ISO files
Microsoft has released the Windows 10 21H1 ISO files, which are now available for download. Here are the links (valid for both Home and Pro) to download Windows 10 May 2021 Update:

Just-Released Windows 10 v21H1 Gets Its Own List of Known Issues Minutes After Public Release

Windows 10 May 2021 Update (64-bit)
Windows 10 May 2021 Update (32-bit)
For languages other than English, head over to Microsoft. As these links will expire soon (5/19/2021 5:29:44 PM UTC), follow the instructions below to easily download Windows 10 21H1, May 2021 Update ISO (HOME and PRO) for your devices:

Head over to the official download site [click this link].
Under Select edition drop-down, click on Windows 10 under May 2021 Update and hit Confirm. [There will be only one Windows 10 option since this works for both Pro and Home editions]windows 10 21h1 iso
Under Select the product language, choose your language > Confirm.
You will now see two tabs to download either the 32-bit or the 64-bit Windows 10 May 2021 Update. Simply click on the right one, and the download will begin.
Windows 10 May 2021 Update is another Service Pack-like release from Microsoft after versions 1909 and 20H2. This means for those of you who upgraded their devices to versions 2004 or 20H2, it will be delivered like a monthly cumulative update, significantly reducing the downtime and improving update experience.

As always, we don't recommend installing a new version of Windows 10 on your primary devices as soon as it's delivered. Waiting a couple of months helps see if there are any issues that could impact your devices or if your device will get into some compatibility troubles.

You are saying this is still the beta version ?

Hello
Congratulations!
But what will users write who do not install?
This is not yet the official release of 21H1 so please do not force updates if there is no certainty that the installation will succeed because it is normal
For security, the installation is only for some computers!