You are not alone finding that the latest update to Windows 11, packaged as a security update, is failing to install. Based on industry news, however, you might just be lucky that it’s not working. Slashgear reports, for example, that “Windows 11 users are advised to avoid a new system update from Microsoft after some were left with computers that refused to boot. The update in question, KB5074109, is also breaking other areas of the operating system for some. Microsoft is aware of the situation.”
Given the extraordinary complexity of managing every single system configuration with its patches, this isn’t the first time that Microsoft has released a problematic update. This doesn’t mean that you shouldn’t spend a few minutes ensuring that everything else on your computer is updated, however, to minimize any issues or problems. This is also not a major system release, so you’re not missing out on cool new features. Let’s have a closer look…
START IN SETTINGS > WINDOWS UPDATE
The logical place to start our exploration is in Settings. Navigate to Windows Update and see what’s in the queue. Most likely your system will again try to install KB5074109, as mine is doing:

It downloads, it installs almost to 100%, then Settings displays:

No point in retrying, it’s been failing for a few days now. But are you in trouble if that’s not up to date? No.
WINDOWS DEFENDER STATUS
One place you check if you’re worried about malware is Windows Defender. Launch the program, then go into the Virus & Threat Detection area. Scroll down and you should see something similar to:

Notice the date of the latest Virus & Threat Protection update: today! As long as that’s keeping updated, you’re safe. If you’re running a separate or additional antivirus program, ensure it’s updated too.
BACK TO SETTINGS
Back in the Settings program, it’s informative to check the Update History section:

If your history list is empty or doesn’t reflect any updates for the last few months, you might have a problem. Manually check for available updates again, and if there aren’t any other than the one you can’t install, you’re skipping updates. In that instance, it might be worth taking your PC to a local expert to diagnose what’s happening.
CHECK YOUR VERSION OF WINDOWS 11
The update history window shows the current version of Windows on this PC, but let’s do this more formally. In Settings, go to the top, then choose System > About and scroll down to find “Windows specifications”:

It’s showing that this computer is running 25H2, specifically OS build 26200.6901. Is that the latest? You can always identify the most recent release version number at the official Windows 11 Release Information Page:

It’s poorly formatted, but a bit lower down on the page is a table with the information you seek. To make it readable, I’ve chopped out a column of data (as denoted by the dashed line):

I’m running the version in the “General Availability Channel” and the topmost entry is 25H2. The build is slightly newer than what I have (my PC has build 26200.6901, while this shows 26200.7628. That might reflect the missing security update).
My conclusion: This PC is fine for now. It’s the latest OS version and has the latest malware and virus definitions. There are ways to force a system update, but given the industry buzz about the risks and dangers of the current security update, I suggest it’s better to simply check System Updates every 4-5 days and wait until it can successfully install through the usual channel.
Pro Tip: I’ve been writing about Windows for years and have quite an extensive Windows 11 help area. Please check it out to find lots of additional tutorials and guides while you’re here. Thanks!