I had a similiar thing happening. Did some rough calculations and found out system was only using something like 40gb for real, rest was some kind of bug
Have since switched to Evolution X rom and I'm very glad I did
Factory resetting the phone should fix it (this will delete all your data so make backups if you want to keep some things!). I'm not 100% certain though
Keep in mind that this bug will most likely reappear someday, maybe even sooner than later. So it might be worthwhile to look into custom roms if you're a liitle tech savy and/or willing to learn a little bit. This also is your only realistically achievable option if factory resetting doesn't work
I tried disk usage but just shows a bunch of green squares and nothing related to system files. The biggest files in diskusage were whatsapp videos of 14mb.
If you have a PC there are some development tools that can help diagnosis, including system files.
Otherwise if you can afford to do so, it is recommended to try resetting to factory settings. You should read about what that involves before doing so.
It must be something related to SD card. I just tried some type of SD Card formating because it was full and now my sd card kinda merged with the system storage. When I remove the SD Card it says 128 of 128gb full. But before opening the screen from the print it says 40gb occupied...
I've recently updated the system too, might be some bug, but I've seen this problem in many other posts from 3, 4 years ago.
I had something similar come up on my Mac mini, out it was something logging a shit ton of details and I uninstalled that and deleted it and it was fine ever since. Might be something similar here
Cached/temp files, maybe? Depending on what's creating those temp files, it could be on the system partition and not in the apps folders. This is common as hell in Windows.