Orbital-selective anisotropy and thermal anomaly in quasi-two-dimensional <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi mathvariant="normal">K</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:mi>Pt</mml:mi> <mml:

Low lattice thermal conductivity ${\ensuremath{\kappa}}_{L}$ and high power factor $\mathrm{PF}$ are essential for attaining superior thermoelectric performance. However, realizing their synergistic optimization in a single material poses a significant scientific challenge. In this work, we systematically investigate the thermoelectric transport properties of the quasi-two-dimensional materials ${\mathrm{K}}_{2}\mathrm{Pt}{X}_{4}$ ($X$ = Br, I) by integrating first-principles calculations, anharmonic lattice dynamics, compressive sensing techniques, and Boltzmann transport theory. Considering strong quartic anharmonicity with self-energy corrections from bubble diagrams within the unified ${\ensuremath{\kappa}}_{L}$ theory, ${\mathrm{K}}_{2}{\mathrm{PtBr}}_{4}$ and ${\mathrm{K}}_{2}{\mathrm{PtI}}_{4}$ exhibit remarkably low ${\ensuremath{\kappa}}_{L}$ of 0.35 and 0.26 W/mK, respectively, along the $c$ axis at 300 K. The strong anharmonicity in the ${\mathrm{K}}_{2}\mathrm{Pt}{X}_{4}$ system originates from the weak bonds induced by K atoms and the antibonding interactions between Pt and $X$. At high temperatures, ${\ensuremath{\kappa}}_{L}$ exhibits an anomalous increase with rising temperature due to the dominance of a glass-like thermal transport channel. Moreover, since the valence-band maximum and conduction-band minimum are dominated by $[\mathrm{Pt}{X}_{4}{]}^{2\ensuremath{-}}$ orbitals along different directions, the electrical transport shows strong anisotropy under doping. At 900 K, optimally doped p-type ${\mathrm{K}}_{2}{\mathrm{PtI}}_{4}$ achieves a $ZT$ of 2.06 along the $c$ axis, while n-type ${\mathrm{K}}_{2}{\mathrm{PtI}}_{4}$ reaches 1.12 along the $a$ ($b$) axis, significantly outperforming conventional thermoelectric materials. These exceptional results demonstrate the outstanding potential of ${\mathrm{K}}_{2}\mathrm{Pt}{X}_{4}$ ($X$ = Br, I) compounds for high-performance thermoelectric applications at elevated temperatures.