We also calculated the thermal transport properties of these materials using the solution of the phonon Boltzmann transport equation (PBTE) as implemented in the ShengBTE code. By default, this approach requires accurate calculations of ionic forces for 2 nd and 3 rd order displacements. The number of structures that must be considered depends on the crystal symmetry and the chosen nearest-neighbour cut-off distance. Therefore, the accuracy, especially for 3 rd order displacements, is crucial for obtaining an accurate description of the lattice thermal transport properties. Figure a-e compares the thermal transport properties of the 2DMs calculated using both DFT and GAP forces, respectively. Overall, the GAP results for all the 2DMs studied are in good agreement with the reference DFT calculations. In addition, the phonon relaxation times calculated with the consideration of 3 rd order force constants throughout the Brillouin zone are also consistent with the DFT results. These findings demonstrate the reliability of our GAP models, particularly for thermal calculations. Zhang et. al 14 fitted a GAP potential for silicene and predicted We also compared the DFT and GAP-generated forces using the HIPHIVE code. As shown in the top row of Figure , the accuracy of DFT and GAP models in determining 3 rd order force constants for lattice thermal conductivity calculations is very impressive. Figure in the Supplementary Materials, which presents relaxation time calculations based on HIPHIVE, also supports the accuracy of our potential. It is worth noting that for such good agreement between DFT and HIPHIVE in phonon relaxation time calculations, the forces calculated by GAP-HIPHIVE for the selected set of displacements must be as accurate as the reference DFT calculations. The fact that the generated GAP potentials achieve this level of accuracy and enable the use of an approximate but more efficient method is noteworthy.