What kind of computations does Ethos-U55 NPU perform? I mean: matrix computation? Trigonometric computation? Multiply-and-accumulate? What types of data is it capable of using? Fixed-point or floating-point? How many bits?
You may wish to explore Cortex-M7 and its FPU:https://developer.arm.com/documentation/dui0646/c/Cortex-M7-Peripherals/Floating-Point-Unit
If you are choosing an MCU be sure to verify that FPU is supported, as it is optional, and so not all silicon may provide it.