I would recommend reading the chapters on Finite State Machines from Object Oriented Design & Modelling - Rumbaugh, et al. Given it was written nearly 30 years

I would recommend reading the chapters on Finite State Machines from Object Oriented Design & Modelling - Rumbaugh, et al. Given it was written nearly 30 years ago - the concepts it puts forward are much closer to the ideas that Kay had than what passes for OO these days.