System storage at 360 GB after deactivating iCloud

Hi,

I just tried using iCloud as somebody shared a huge folder (750GB) with me. It started syncing/downloading automatically. Of course it is a stupid idea to share such big amount of files via iCloud, but anyway. So I cancelled the download and deactivated my iCloud. The result is I suddenly have 360 GB of System data now on my macbook and no way of clearing it up. I know that before this iCloud experiment I had plenty of free space on my drive. Checked all the possible caches and other possible places in Libraries. No use whatsoever. There are no folders on my computer that would be taking up that much space. Yet the System folder is cluttering up space and I am finding no other way to clear other than format/reinstall, which would be a bummer as I would need to set up all of my Adobe programmes settings, fonts, logins etc...

Apple doesn't offer a solution online, maybe some of you have had a similar issue here?