I am trying to automate SQL developer connection using FlaUI and windows accessibility insights tool but windows accessibility insights tool not detecting some UI element[plus[green button]].

I am expecting that accessibility insights tool detect [plus_green_button] and return automation_id.
When Accessibility Insights for Windows can see a window but not its individual elements, that usually indicates that you're attempting to scan an elevated process (eg, one you're launched with "Run as Administrator") from a non-elevated Accessibility Insights process. Try either running the application being scanned as a non-administrator or, if that is not possible, running Accessibility Insights for Windows using "Run as Administrator".