In this paper, we study properly biharmonic hypersurfaces in the Minkowski 4-space E4 1 that are invariant under the action of some Lie groups of isometries. Using the symmetries imposed by Lie groups, we provide a local classification of such hypersurfaces according to the causal character of the orbits and the ambient semi-Euclidean metric. Explicit parametrizations are obtained for non-degenerate cases, and geo metric properties such as the mean curvature, second fundamental form, and biconservative condition are analyzed in detail. Several examples are presented to illustrate the theory. Our results generalize previous known classifications of biconservative hypersurfaces in Euclidean and Lorentzian settings and highlight the interplay between group symmetry and higher order geometric constraints.
