twrp – How to reduce the abnormal size of internal storage in ALE-L21

I have a custom ROM and TWRP and rooted the phone, but the operating system was recently installed and even without a custom ROM, I can clearly see that my internal storage value is abnormally large because in Titanium Backup, it doesn't show such a large size for the internal storage or for the system partition and I have approximately 16 GB in the specification value of my phone, what is the problem, I need to solve it because some applications must be installed in the internal storage.
Internal storage information of the operating systementer the description of the image here