Sometimes you need to quickly create a usable ICNS file to deploy a macOS application.
An Automator script can be used to provide a Quick Action that will do the heavy lifting for you.
Once saved, you can right click on an image file, select Quick Actions -> Create ICNS from Image. A few seconds later you should have an ICNS in the same folder
#!/bin/bash
INPUT="$1"
# Extract folder and base name
DIR=$(dirname "$INPUT")
BASENAME=$(basename "$INPUT")
NAME="${BASENAME%.*}"
ICONSET="${DIR}/${NAME}.iconset"
mkdir -p "$ICONSET"
# Generate all required icon sizes
sips -z 16 16 "$INPUT" --out "$ICONSET/icon_16x16.png"
sips -z 32 32 "$INPUT" --out "$ICONSET/icon_16x16@2x.png"
sips -z 32 32 "$INPUT" --out "$ICONSET/icon_32x32.png"
sips -z 64 64 "$INPUT" --out "$ICONSET/icon_32x32@2x.png"
sips -z 128 128 "$INPUT" --out "$ICONSET/icon_128x128.png"
sips -z 256 256 "$INPUT" --out "$ICONSET/icon_128x128@2x.png"
sips -z 256 256 "$INPUT" --out "$ICONSET/icon_256x256.png"
sips -z 512 512 "$INPUT" --out "$ICONSET/icon_256x256@2x.png"
sips -z 512 512 "$INPUT" --out "$ICONSET/icon_512x512.png"
sips -z 1024 1024 "$INPUT" --out "$ICONSET/icon_512x512@2x.png"
# Create the .icns file in the SAME folder as the input
iconutil -c icns "$ICONSET" -o "${DIR}/${NAME}.icns"
echo "Created ${DIR}/${NAME}.icns"