Clear cache for the system (you'll have to restart in recovery to do that). Part of that additional system storage may just be cache files that the system failed to clean up.
NEVER run an app that says "Clean up ROM, RAM memory, SD card, running process" - ROM is "Read Only Memory", it can't be "cleaned up. Android doesn't want RAM cleaned up, it wants as much used as possible (see
Multitasking the Android Way (technical) if you want to learn why) - Android isn't Windows. And you definitely don't want to "clean up" a running process in any computer - that just causes the process to crash.
It also says, "Clean up duplicate files and photos". Only you know whether a picture or other file is a duplicate, so no app can automatically delete duplicates. And "Clean up other garbage like obsolete files, residual files, empty folders, app leftover" is nonsense - how does the app know if a file you haven't used in 10 months is obsolete? Maybe you only use it on Christmas, nut want it in the phone. "Residual files"? Except for cache, there's no such thing. There may be empty folders that you want kept. And "app leftover" is another "words that mean nothing".
If I hadn't checked the developer name, I'd think it was Cheetah - they don't understand how Android works either.
Clean up the caches (one for each app, one for storage and one in recovery), and uninstall apps and delete files by yourself. You don't need an app deleting things you want then, when you come here and find out that you can't restore them ... well, you figure that one out.
But at least back up the entire phone before playing around in it. See
Backing up an Android Device.