It is possible to create a system so complex no one understands it. The world economy is one such system. That’s why there is so much debate about it.
Another system is a modern car. Likely no one understands everything about each part of the car. Some understand the engine. Some understand the software. Some understand the structural design. Some understand the interior choices. No one individual understands it entirely.
In your company, there are likely systems that evolved over time that are so complex that no one understands them either. Perhaps a database with different fields and options that were added over a decade by different people and no one knows what they mean any longer.
What is important is to understand when the system is so complex that no one can function with it. The car, for example, is complex, but it is easy enough to use it and extract value from it. That’s not necessarily true for certain systems and functions in our work.
If they are both complex, and not providing enough value, then simplify them.