In Windows 11 and for certain themes, all windows screens like explorer had transparent borders and made it difficult to differentiate between two explorer screens on top of each other. Adding a certain colored border will help to differentiate more clearly and avoid accidental clicks. To set borders on Windows Explorer, you can follow the steps below:

Go to “Settings” and select “Personalization” In the Personalization window, click on “Colors” to expand to below view Scroll down to the section labeled “Show accent color on title bars and windows borders” and enable the toggle switch