How can I organize desktop screenshots on iMac?

Screenshots can be treated like any other file or folder that is on your desktop.

In the menu strip at the top of your desktop,

• Do View > Sort by > None

then

• Do View > Clean Up. Don't do "Clean Up By ..."
• Then move the screenshots & any other files or folders where you want to place them on your desktop.

What macOS version?

The Screenshot App has an option for telling it WHERE your screenshots go without your having to manually move them. See this:

Take screenshots or screen recordings on Mac - Apple Support

Note the image near the top. The "Options..." button lets you create a folder for screenies and place it wherever you wish. Doing that has saved me a lot of time.

I hate having screenshots, icons and other junk plastered on my desktop.

What I do is put the screenshots that I want to save into a Folder named Screenshots and trash the rest.

Tell me what you are trying to accomplish.

• From your first question it appeared you wanted to arrange things on your desktop.
• Now it sounds more like you want to get information about a particular screenshot file.