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Windows 11 has introduced a new mechanism to denote when an application needs focus:
"When a background activity from an app requires attention, the app will flash on the Taskbar to get your attention. In Windows 11, we have updated this design so that it still grabs your attention but with a calming treatment that minimizes the impact of unwarranted distractions. The subtle flashing eventually stops, and you will see a slightly red backplate and red pill under the app icon continuing to note a background activity needs your attention."
After an E-Prime run, another open application may require focus before being able to be maximized in the Taskbar.
In the image above, the Folder Explorer requires attention. To do so, minimize E-Studio and give focus to the Folder Explorer until it is no longer red.
For more information, see Announcing Windows 11 Insider Preview Build 22000.100 | Windows Insider Blog.