I am sorry but I don't see the actual issue.
I must be dumb.
Ok got it. I am confused because your app list seems unfinished.Check how much used space it says I have and then check below and add the things and check how much actual space I'm using. You will be left with like 5gigs of space which are nowhere to be seen, either being used by other or documents as shown in iTunes. The problem is I have no documents or anything using that space, it's just probably something I deleted and iOS doesn't mark the space as free.
Only solution is doing what someone said and downloading big file that doesn't fit my free space and it kinda triggers the cleanup process or backing up and restoring from backup.
Ok got it. I am confused because your app list seems unfinished.
There are various stuff occupying storage when you cannot do anything, such as multiple corrupted app downloads, unrecognizable music files and so on. Cache is just half of the story.
No one knows. By far the best way is to backup, restore, and restore backup. I did it once before but only freed 2GB. Not too much given I am using 128GB device.And that's exactly my point, why does iOS still not have a clean cache/corrupted downloads/any other crap using the free space?