I have a code in which I directly specify the path to the folder via EMBED, but I know that you can somehow point to the folder and then just write the file name, but I don't know how to do it
template.ParseFS(resources.Content, "*png, *jpg")
As you are using Fyne resources you can generate them directly from the filesystem and avoid the boilerplate by using
fyne bundle -o planetResources.go resources/img/planets/