Hi Siebe,
You are correct to say that all happens due to causes and conditions without there being an agency for all this to happen. I agree with you and this is the cause and effect (hethu pala) that is exposed by the Buddha. But I don’t see this as anatta.
When it is said that form is anatta, the form here (rupa), does not refer only to the bodily form, but includes all forms; living and non-living. So, if you take anatta to mean “there being no agent who controls” we can easily see the connection with living forms. But what is the connection with non-living forms?
For example, a book is a type of form. Do we need anyone to explain to us that there is no agent that controls the book? Anyone, even a young child, can understand that there is no agent that controls the book.
Is a book non-self? Yes, anyone will tell you that a book is not themselves. Does the book have a self? Is there someone who controls the book? Don’t these questions seem a bit foolish?