not able to remove icon coming up on desk bar at starting my iMac

Apple > System Preferences > Dock & Menu Bar > uncheck “Show Recent Applications in Dock”

https://support.apple.com/guide/mac-help/open-recently-used-items-on-mac-mchlp2724/mac

The icon is in the area of recently used items. Try dragging the icon to the bin.

Goto users & groups in System Preferences, against your name look at the login items and if you can recognise what’s loading this icon just remove it.

What Icon?

You need to better explain what it is or post a screenshot.