Is KB5086672 safe to install or is it another mess. And why is Microsoft Incompetent?

Hi, I'm Bernard. I'm happy to help!

The KB5086672 is a cumulative update which is for fix and improves the previous update, and yes, this is safe for your device. Moreover, to make sure that there are no issues, I suggest creating a system restore point to make sure you can go back to the previous state of the PC if you experience any issues.

To create a restore point:  https://support.microsoft.com/en-us/help/4027538/windows-create-a-system-restore-point

The safety or quality of update KB5086672 is not covered in the available context, so no statement can be made about that specific update.

For Windows updates in general, the context shows that:

• Cumulative and security updates are designed to deliver security fixes and reliability improvements, and they are cumulative (each new one includes previous fixes). Examples include Windows 10 cumulative updates and security updates for Microsoft Edge and Internet Explorer.
• Microsoft sometimes releases additional updates to improve the reliability of Windows Update itself and the update client.
• When issues occur after an update, installing the latest cumulative/security update can resolve them, as shown in the Dymo/Edge printing scenario where a later security update restored functionality.

Because the context does not mention KB5086672, there is no supported way here to say whether that specific update is “safe” or “a mess.”

References:

• Cumulative update for Windows 10: August 9, 2016
• MS16-024: Cumulative security update for Microsoft Edge: March 8, 2016
• August 11, 2020—KB4571689 (OS Build 15063.2467)
• Cumulative update for Windows 10: November 8, 2016
• Cumulative update for Windows 10: August 11, 2015
• Latest Edge update seems to have broken the ability to print to Dymo labelwriter 450 - Microsoft Q&A