My app is set to use .net maui 7.
I had error messages like yours, but if you keep "Clean Solution" and "Rebuild Solution" the error eventually disappears (Microsoft even writes to do so in their description :-)
But now the icon thing is working on my side !?!
Wonder if it is only the Droid/iOS OS' that remember the old icon, I tested the app with the original MAUI icons ????