Depends how much neuron density you have in the part of the brain that handles this. It’s mostly about memory, being able to accurately and quickly remember all the little steps you have already done and what the results of those steps were. Then just keep going one digit pair at a time keeping in mind all the results so you can deal with the carry overs.

But the whole reason we can focus on teaching everyone shortcuts for smaller math now is because we do literally always have a calculator on us now. So while it’s still good to know how to do bigger math more efficiently, you’ll never catch up to a calculator anymore. It’s more important that they know the foundational concept well enough to move on to the next step now rather than practicing doing big math faster and faster. Can leave that to the individuals with talent in the area.