Takuya MatsuyamaI had to make another .icns file in order for my app to match the icon style on macOS Big Sur. Here is how to make .icns file from png files. You don't need to use any app for doing it but only a built-in command-line tool.
Make a folder named ***.iconset (e.g., desktop-icon.iconset) and prepare files like so:
> ll
total 49976
drwxr-xr-x 13 user staff 416 Jan 12 19:23 desktop-icon.iconset/
> ll desktop-icon.iconset/
total 1376
-rw------- 1 user staff 10416 May 6 2019 icon_128x128.png
-rw------- 1 user staff 26457 May 6 2019 icon_128x128@2x.png
-rw------- 1 user staff 665 May 6 2019 icon_16x16.png
-rw------- 1 user staff 1651 May 6 2019 icon_16x16@2x.png
-rw------- 1 user staff 26457 May 6 2019 icon_256x256.png
-rw-r--r--@ 1 user staff 91117 Jan 12 19:06 icon_256x256@2x.png
-rw------- 1 user staff 1651 May 6 2019 icon_32x32.png
-rw------- 1 user staff 4331 May 6 2019 icon_32x32@2x.png
-rw-r--r--@ 1 user staff 91117 Jan 12 19:06 icon_512x512.png
-rw-r--r--@ 1 user staff 422658 Jan 12 19:21 icon_512x512@2x.png
The folder content looks like this:
Generate .icns file:
> iconutil --convert icns desktop-icon.iconset
Then, you should get a file like so:
Hope that helps!
