A complicated solution can create dependence on the person who understands it.

A system only one person understands turns that person into a permanent requirement. It feels like security to them and it is a liability for everyone, including them, because they cannot leave, take time off, or move on without the whole thing becoming a problem. The complexity has quietly created a dependency nobody chose.

Check what in your work only you could pick up. Then simplify or document it until someone else could. It protects the organization and it also protects your own freedom to move.