  Within the framework of relative and absolute quantum field theories (QFTs),
we present a general formalism for understanding polarizations of the
intermediate defect group and constructing non-invertible duality defects in
theories in $2k$ spacetime dimensions with self-dual gauge fields. We introduce
the polarization pair, which fully specifies absolute QFTs as far as their
$(k-1)$-form defect groups are concerned, including their $(k-1)$-form
symmetries, global structures (including discrete $\theta$-angle), and local
counterterms. Using the associated symmetry TFT, we show that the polarization
pair is capable of succinctly describing topological manipulations, e.g.,
gauging $(k-1)$-form global symmetries and stacking counterterms, of absolute
QFTs. Furthermore, automorphisms of the $(k-1)$-form charge lattice naturally
act on polarization pairs via their action on the defect group; they can be
viewed as dualities between absolute QFTs descending from the same relative
QFT. Using this formalism, we present a prescription for building
non-invertible symmetries of absolute QFTs. A large class of known examples,
e.g., non-invertible defects in 4D $\mathcal{N}=4$ super-Yang--Mills, can be
reformulated via this prescription. As another class of examples, we identify
and investigate in detail a family of non-invertible duality defects in 6D
superconformal field theories (SCFTs), including from the perspective of the
symmetry TFT derived from Type IIB string theory.
