I am still trying to rationalize what you meant, and you haven't responded, so I am left with trying to figure out your meaning.
So, last night I came across this thought...
Perhaps you think using IrfanView as an opened window where you then just paste in your screenshots is going to capture your mouse cursor. Well, as you found out, that doesn't work.
What I meant is that there is a screen Capture (just press the "C" key, or select the command Options>Capture). At that time you will see the Capture Setup window.
In the Capture setup window you make your settings to "Include mouse cursor." In that same window you also select the destination folder, or just have the capture area automatically placed in the viewer window. Also, if you decide to go with the save as a file, you can specify what directory to place the captures and what format to use. Then click the [Start] button. The IrfanView window will minimize, so it looks like it closed - but it hasn't. It is running and waiting for your hotkey press.
I use the Capture quite often while I test software where I work. It is an easy and fast method to grab images off the screen as fast as I push a key. I could even set it as an automatic timer.
IrfanView is a really great tool.
I sure hope that straightens it out, if you were having some misunderstanding about capturing the mouse cursor.