It's kind of a cliche at this point - but a good start is 'The Toyota Way', which talks about developing people. I'd also be interested if you can find an authoritative source. I just have a lot of news articles - a good overview is this one in industryweek (https://www.industryweek.com/operations/tesla-vs-tps-seeking...).
The basic principle is somewhat obvious - automation is efficient, but inflexible. That often leads to machines sitting idle, or the overproduction of unsaleable stock. So it's a kind of poison chalice - it looks like you'll reap huge profits, but if your car doesn't sell well, you're screwed. If you invest in people instead, you can react to changing economic conditions.
https://www.thedrive.com/tech/26955/inside-toyotas-takaoka-2...
I've been told in the past that the key factor in Toyota success is their relationship with their suppliers. A top notch supply chain with just in time processes bundled with reasonable proxy stocks?
Would love to read about their automation level compared to US or EU companies