Typically I define complexity as a low probability macrostate meaning low entropy. So debris generated from the explosion has a high probability of randomly occuring, while a new car has a very low probability of randomly occuring.
Following this definition you arrive at a formal definition of complexity that is intuitive.
Imagine a tornado that randomly reconfigures everything in it's wake. The more complex something is the less likely the tornado is going to reconfigure everything into that thing. So it is very likely for a tornado to reconfigure things into debris and extremely extremely unlikely for the tornado to reconfigure everything into a brand new car. A tornado reconfiguring atoms into a car seems to be impossible but it is not, it is simply a low probability nearly impossible configuration.
Therefore the car is more complex then exploded debris.
Think about this definition because it also aligns intuitively with the effort required and technical complexity of any object. The more effort and technical complexity it has the lower chance it has of a tornado randomly reconfiguring atoms to form that object. Thus that object is more "complex".
Whatever your definition is, the quote saying complexity cannot be created or destroyed is fundamentally from any perspective usually not true. If you want to define it as simply microservices or monoliths it still doesn't make sense. Whose to say that when converting a monolith to microservices that complexity remains conserved? Likely the complexity rises or lowers a bit or a lot. Complexity doesn't remain the same even if you use informal and inexact fuzzy definitions of complexity.