can't find screenshots

I see that the Support Article which I previously linked doesn't completely describe how to access the "onscreen controls" Go to your Utilities Folder, and select the "Screenshot" application:

When the application opens you will see the following controls at the bottom of the screen:

The "Options" selection can be used to make the following selections:

I recommend using the "Desktop" option.

Since your screenshots are currently being placed in the Pictures folder you can find them in your Macintosh HD>Users>yourusername>"Pictures" folder. You can also use "Spotlight" to find your "Pictures folder.

According to: How to take a screenshot on your Mac - Apple Support

"Change the settings

Click Options in the onscreen controls to change these settings: 

• Save to: Choose where your screenshots are automatically saved, such as Desktop, Documents, or Clipboard.
• Timer: Choose when to take the screenshot: immediately, 5 seconds, or 10 seconds after you click to capture.
• Show Floating Thumbnail: Choose whether to show the thumbnail. 
• Remember Last Selection: Choose whether to default to the selections you made the last time you used this tool.
• Show Mouse Pointer: Choose whether to show the mouse pointer in your screenshot."