Edit: I found out that the method described below does not work. If you try to imagine doing this, you will get a bunch of mistakes. I will leave it here, so no one makes the same mistake.
For simplicity (with the Images.xcassets folder 1), I deleted the Images.xcassets folders created when I created the monitoring application, then moved to the existing Images.xcassets and added new images (you can do this by turning on the Apple Watch icon in the Attribute Inspector). Then I just included this folder in the app for the Apple Watch app (and not the purpose of the extension).
Having done this, I see that the icon is displayed in the Apple Watch application for my application (you may need a reset simulator to display it).
The only drawback of this approach is that it will add unused icons to your watch application, which will increase the file size of the application. For my case, the added size is less than 1 MB, so this is not a huge deal.
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