In this definition of not-self below, it begins the premise that all phenomena is devoid of self but that is a premise only in this statement because there is no proof given. One is expected to accept it as an assumption.

All the same I could begin the assumption that phenomena is full of everything and thus there is self everywhere, surfacing and disappearing constantly. The lack of constancy does not prove that there is no self or that everything is nothing.

The contention that the phantom personality is born of ignorance and delusion does not remove the instance of self. In fact once someone states that it is bound up with suffering, that means there is a target or self and thus the denial of it is absurd.

anattã: Not-self; the truth that all phenomena are devoid of anything that can be identified as “self”. This means that none of the physical and mental components of personality (the 5 khandhas ) make up an entity, either individual or collective, nor can a self-entity be found anywhere within the heart (citta). Therefore, what is experienced as being an abiding self is no more than a phantom personality born of ignorance and delusion – inherently transient, unstable, and bound up with suffering

That is from the book at this link:

https://inselfyoga.com/s/bx_forum_files/mqfnqkxzpfvekjczuubdunq534pvwxit.pdf