Rare‐Earth‐Doping Induced Two‐Dimensional Entropy‐Stabilized Metal Sulfides With Strong Polarization‐Dominated Dielectric Loss via Electronic Coupling

High‐entropy materials have emerged as a versatile platform for tailoring physicochemical properties through compositional complexity, while their potential for electromagnetic wave attenuation remains underexplored. Here, we report a two‐dimensional high‐entropy sulfide system with tailored electronic structure achieved via rare‐earth element doping, in which lanthanide ions (Tb and Pr) with high coordination characteristics are incorporated to modulate crystal phase, morphology, and dielectric behavior. The synergistic hybridization between the f‐ orbitals of rare‐earth elements and the d ‐orbitals of transition metals facilitates charge redistribution, thereby enhancing interfacial and dipolar polarization losses and promoting efficient electromagnetic wave attenuation. As a result, the optimized two‐dimensional high‐entropy sulfide system exhibits a minimum reflection loss of −41.81 dB at 16.96 GHz with a thin matching thickness of 1.5 mm and achieves a broad effective absorption bandwidth of 4.7 GHz at 2.22 mm. Furthermore, radar cross‐section (RCS) simulations were performed to compare coated configurations with bare material devices under different geometric structures, providing a comprehensive evaluation of the material's potential for practical applications. This work introduces a rare‐earth‐driven two‐dimensional structural high‐entropy design strategy for electromagnetic wave attenuation, offering new insights into leveraging lanthanide chemistry to achieve high‐performance microwave absorber even electromagnetic functional devices.