  We characterise subhomogeneity for twisted \'etale groupoid C*-algebras and
obtain an upper bound on their nuclear dimension. As an application, we remove
the principality assumption in recent results on upper bounds on the nuclear
dimension of a twisted \'etale groupoid C*-algebra in terms of the dynamic
asymptotic dimension of the groupoid and the covering dimension of its unit
space. As a non-principal example, we show that the dynamic asymptotic
dimension of any minimal (not necessarily free) action of the infinite dihedral
group $D_\infty$ on an infinite compact Hausdorff space $X$ is always one. So
if we further assume that $X$ is second-countable and has finite covering
dimension, then $C(X)\rtimes_r D_\infty$ has finite nuclear dimension and is
classifiable by its Elliott invariant.
