Why is that the only definition of complex? Most complexities in business comes from process complexities or even business complexities. I once worked with a software as a service company that provided software for the car repair industry. We had to translate these rules for both the repair shop and the car owner.

https://www.railinc.com/rportal/documents/18/260737/CRB_Proc...

There is more to it than this.

Did we have millions of users? No. The rules were complicated, and most processing happened once a month. There is a central exchange that both sides go through.

I’ve had three jobs in healthcare. While the scale of users weren’t anything crazy. The business requirements were complex.

Because that definition of complex opens tons of doors to companies that are leading tech industry?

My background has always been in Enterprise software (healthcare, insurance, BI, etc, almost a decade). At some point I felt that translating complex biz reqs are no longer interesting.

I find dealing with scalability (and hopefully build my own system library) is more interesting and challenging that the Enterprise market.

Consistent Hashing algorithms, Distributed Systems, System programming, build your own programming languages, maybe build my own messaging/background processing?

YMMV.