You write that 246GB has been used out of 256GB, then there is still 10GB left. I have not even used 10GB yet on my iPhone, but what I want to say with it is that there is still plenty of space available, therefore the system has not started to clean up yet.
All the data in the system is data from all your apps. That data means that your apps run as they should, and have smaller load times.
But if you are worried as you say you are - then you can find big "test files" on the web that you can download. You do not need to use the files, but when the files download, the system will start maxing out the last space and iOS will be forced to start cleaning up. Remember to be connected to WiFi if you have a limited mobile data plan. I would not recommend it because it is not necessary, but it is an option. You can also turn it off and on again, it also cleans up the worst cache files.
You can also go to:
Settings -> General -> iPhone Storage
There you can review your apps and see if there are any apps you do not use that take up a lot of space.