The application icon for my data wrangling software looks like this on a Mac up to macOS 15.x:

However, Apple has once again nuked everything from orbit. Now it looks like this in macOS 26 Tahoe when the application is inactive or if you choose any Icon & widget style apart from Default:

Thanks Apple. It is such a joy to develop for Mac.

With some help from a designer and hours of going around in circles, I have finally managed to fix things to support the new ‘liquid glass’ look. This is how it should look in the next release, depending on the setting in Appearance>Icon & widget style:

I’m not convinced it is an improvement in terms of usability. But, at least my app icon doesn’t look like shit.

What you need to know

The new macOS 26 icon format is .icon. It is a folder full of various resources and is totally different to the old .icns format.

The .icon file can be created by Apple Icon Composer. I used a freelancer on Fiverr who did a good job of converting my existing vector artwork and was very cheap. The .icon file should contain a maximum of 4 groups (which seem to be like layers) other it won’t compile to a resource properly.

Note that macOS hide the extension of .icon folders by default, which was a source of some confusion.

The .icon file then has to be processed into an Assets.car file using actool. For example:

xcrun actool application.icon --compile ./icons/macosx --output-format human-readable-text --notices --warnings --errors --output-partial-info-plist temp.plist --app-icon Icon --include-all-app-icons --enable-on-demand-resources NO --development-region en --target-device mac --minimum-deployment-target 26.0 --platform macosx

You will need to change the bold parts above, as appropriate.

I had to update my Mac laptop to macOS 26, Xcode 26 and the macOS 26 SDK for the above to work.

You can check the Assets.car file using assetutil to create a .json file listing the contents:

xcrun --sdk macosx assetutil --info ./icons/macosx/Assets.car > ./icons/macosx/temp.json 

You will need to change the bold parts above, as appropriate.

Then you need to reference the new icon in your existing application .plist file. For example, add at the same level as CFBundleGetInfoString:

<key>CFBundleIconName</key>
<string>application</string>

You will need to change the bold part above, as appropriate. I believe the string value if based on the file stem of the original .icon file. But I’m not 100% sure about that. Look at the .json file produced by assetutil for clues. Mine contained this:

The temp.plist file generated by actool is apparently supposed to give you a .plist file that refers to the icon resource. It didn’t and was completely useless.

Then place both Assets.car and your old .icns file in the Resource folder of your application (before you sign it). That way it should look ok on both macOS 26 and earlier OSes.

If you develop using XCode, it will probably do some of the above for you. I develop in C++/Qt using Qt Creator, so I had to do it all manually.

I was able to generate the Assets.car on macOS 26 and then incorporate it into the build on my macOS 12 development machine.

I hope the above saves someone a few hours. Now I need to repeat the process for PerfectTablePlan.

You might also find this post useful (where I got some of the information):

https://www.hendrik-erz.de/post/supporting-liquid-glass-icons-in-apps-without-xcode