<p>It has been reported that hybrid nanofluid-assisted machining performs better than mono nanofluids. However, some solid lubricants (nanoparticles) transform to another phase (like MoS₂ to MoO₃) at high temperatures, thereby providing a poor lubrication effect during machining, whereas hard nanoparticles like diamond or SiC create scratches on machined surfaces. This study aims to develop a potential novel hybrid nanofluid by simultaneously dispersing ceramic nanoparticles (hBN) and soft metallic nanoparticles (Cu) in lubricious coconut oil, ensuring their chemical inertness at high temperatures without compromising the solid lubricant’s properties. Thermophysical properties such as thermal stability, thermal conductivity, viscosity, viscosity index, wettability, and tribological performance of the proposed cutting fluids have been evaluated. Furthermore, their performance in end milling of Incoloy 925 is investigated in terms of specific cutting energy, carbon emission, surface roughness, surface topography, and tool wear. Formulated hybrid nanofluid performs better than dry, base oil, and mono nanofluid. The sustainability of machining performance is evaluated with a triple bottom line (TBL) approach, and it is found that product sustainability index (ProdSI) under hybrid nanofluid (HNMQL)–assisted machining scores 3 times of oil (MQL)–assisted machining and 1.85 times of mono nanofluid (NMQL)–assisted machining. It discusses the problems with a group of cutting mediums and looks at what might be possible for better and more sustainable cutting processes in the future. The proposed cutting fluids with a suitable setup can be used in industrial applications, such as the machining or lubrication/cooling (automobile) sector.</p>