This is handled by the inverter and charging modules, some use FPGA chips others use dedicated ASICs, but it doesn't require anything wild in terms of raw compute power, mostly up to having good algorithms to handle the situations correctly. Nothing more than a modern ICE engine which needs to very precisely manage intake and exhaust cam phasing, ignition timing, intake pressure, and multiple injections per cylinder/cycle along with monitoring a multitude of sensors to keep everything in tolerance. In terms of simplicity, the first automobiles at the turn of the century were electric before the ICE caught on thanks to the advent of the electric starter and limitations in battery technology at the time.

I am not an engineer, but I imagine keeping multiple DC motors running efficiently/in sync together while outside influences change by the second isn’t easy.

It's easy. I'm not a professional engineer, but I'm close enough to know this one.

A typical phone CPU can make adjustments to an output many tens of millions of times a second. It might be "only" thousands for the 10 cent toaster CPU. If it had to model and predict the road ahead somehow, that'd be harder, but just responding to changes as the wheels hit them requires some trig operations at most.

As for the other bit, electric motors are way, way simpler than IC engines, just intrinsically. It's a clever arrangement of magnets, vs a block of metal that has to produce and withstand constant fuel explosions using barely-standardised fuels, and then convert the resulting energy into rotation at the gear ratio of your choice, and do it for years without breaking. With electrics, the magic is all in the battery chemistry.