Have you edited:
mnt/ext1/system/config/desktop/view.json
You'll need to add all the apps you want to change the icons for to the json file.
You need to be careful with the formatting, otherwise the menu will not show at all. if you do mess it up, just delete the json file and reboot and the default one will be generated anew.
There's an example view.json file for my device within the zip file in this
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