My S20 Ultra started complaining it was running out of space randomly. I deleted about 11GB of games and thought not much else of it. Then, a short while later my phone was full again!
I presume it's some error log or something getting out of control but I got to the state where the system was using Nearly 42GB of storage (see screenshot). I deleted as much as I could again but it kept filling up. I tried to take another screenshot and hit the screenshot bug and my phone rebooted (😂). When it came back the system was only using about 20GB...