Given the global phase-down of HFCs (like R-404A and R-134a), a modern must dedicate a full chapter to A2L refrigerants (e.g., R-32, R-454B) and natural refrigerants (CO2 / R-744, ammonia / R-717, propane / R-290).

This sounds like a great project! Since refrigeration covers everything from basic physics to complex industrial systems, the "best" post depends on who you are trying to reach.