  Given the Hamiltonian realisation of a topological (3+1)d gauge theory with
finite group $G$, we consider a family of tensor network representations of its
ground state subspace. This family is indexed by gapped boundary conditions
encoded into module 2-categories over the input spherical fusion 2-category.
Individual tensors are characterised by symmetry conditions with respect to
non-local operators acting on entanglement degrees of freedom. In the case of
Dirichlet and Neumann boundary conditions, we show that the symmetry operators
form the fusion 2-categories $\mathsf{2Vec}_G$ of $G$-graded 2-vector spaces
and $\mathsf{2Rep}(G)$ of 2-representations of $G$, respectively. In virtue of
the Morita equivalence between $\mathsf{2Vec}_G$ and $\mathsf{2Rep}(G)$ --
which we explicitly establish -- the topological order can be realised as the
Drinfel'd centre of either 2-category of operators; this is a realisation of
the electromagnetic duality of the theory. Specialising to the case $G =
\mathbb Z_2$, we recover tensor network representations that were recently
introduced, as well as the relation between the electromagnetic duality of a
pure (3+1)d $\mathbb Z_2$ gauge theory and the Kramers-Wannier duality of a
boundary (2+1)d Ising model.
