M4 Max doesn't even disclose TFLOPS so no clue where that website got the numbers from.

TFLOPS can't be measured the same between generations. For example, Nvidia often quotes sparsity TFLOPS which doubles the dense TFLOPS previously reported. I think AMD probably does the same for consumer GPUs.

Another example is Radeon RX Vega 64 which had 12.7 TFLOPS FP32. Yet, Radeon RX 5700 XT with just 9.8 TFLOPS FP32 absolutely destroyed it in gaming.