Potentially unwanted applications (PUA) are a category of software that can cause your device to run slowly, display unexpected ads, or at worst, install other software which may be more harmful or annoying. PUA isn’t malware, but it is software that you often don’t need and probably don’t want.
In the Windows 10 May 2020 Update we added Potentially Unwanted App blocking for everyone running Windows 10, but customers who wanted to use it still had to turn it on.
Starting in early August 2021 we’ll begin turning it on by default to make it easier for you to keep your systems performing at their best. If you’d like to turn it off, or back on, for any reason you can do so by going to the Windows Security app > App & browser control > Reputation-based protection.
For more information see Protect your PC from potentially unwanted applications.
Source: Potentially unwanted apps will be blocked by default
How to Enable or Disable Microsoft Defender Antivirus Potential Unwanted App (PUA) Protection in Windows 10