I think the entirety of the A-series, M-series and even S-series lines are essentially one chip product line, with different balances of chip area, cost, compute and energy use.

Other than that, perhaps some small form factor related device support differences.

Never been an OS (iOS, iPad, watchOS vs. Mac) distinction from the hardware standpoint.

The only thing I read from M-series in iPads and A-series in the Neo, is the A chip is better balanced in price and power draw for a low cost laptop with a smaller battery.

The M-chip with that balance is the A-chip.