Are you closing the spectacle window after taking a screenshot? I found that you need to keep it open for the image to stay in the clipboard. When I have the time I can check how I've set it up if that doesn't work for you. Although I only copy to clipboard, not save as well.

You'd need to write a script, for example:

#!/bin/bash

# Set the directory where screenshots will be saved
SCREENSHOT_DIR=~/Pictures/Screenshots

# Create the directory if it doesn't exist
mkdir -p "$SCREENSHOT_DIR"

# Get the current date and time in the format MM-DD-YYYY_HH:MM:SS
DATETIME=$(date +"%m-%d-%Y_%H-%M-%S")

# Build the filename using the datetime
FILENAME="screenshot_$DATETIME.png"

# Take a fullscreen screenshot, save it to the specified directory, and copy it to the clipboard
spectacle -f -b -c -o "$SCREENSHOT_DIR/$FILENAME"

# Optional: Notify the user (requires notify-send)
notify-send "Screenshot taken" "$FILENAME saved to $SCREENSHOT_DIR"

You can change the -f to change the screenshot mode. From spectacle --help:

  -f, --fullscreen                        Capture the entire desktop (default)
  -m, --current                           Capture the current monitor
  -a, --activewindow                      Capture the active window
  -u, --windowundercursor                 Capture the window currently under
                                          the cursor, including parents of
                                          pop-up menus
  -t, --transientonly                     Capture the window currently under
                                          the cursor, excluding parents of
                                          pop-up menus
  -r, --region                            Capture a rectangular region of the
                                          screen

Save the script somewhere. It's safest to make it owned by root and put somewhere like /usr/scripts so random user-access programs can't edit the script. Use chmod +x to make it executable.

Then go to Plasma -> Settings -> Keyboard -> Shortcuts, Click 'Add New' -> Command or Script. For the command, give it the path to your script, give it a name click Add and then set a hotkey by clicking the Add butoon.

Oohh this is something I'd love to have as well.