If you're running it as an Automator quick action, then you can close all windows except the frontmost window of the frontmost application by using the code below inside a Run AppleScript action (you can delete any sample code that appears, including on run {input, parameters}...end run:
tell application id "com.apple.SystemEvents" to tell the first process ¬
whose frontmost = true to tell a reference to windows 2 thru -1 to ¬
if exists then tell the value of attribute "AXCloseButton" to click