Can't download anything - Chrome says "Failed - Disc Full" - Tried everything!

I'm having issues downloading anything on my Mac, either on Chrome or Safari. Problem still persists. All started when I downloaded Steam - Then Sid Meiers Civ 6. It kept stopping the download, and when I uninstalled Steam and tried to download again, this is when the "Failed - Disc Full".

I'm having all kinds of issues now, Finder isn't running properly either, nothing is appearing on my Desktop.

I've tried running OmniSweep but it crashed before it's scanned the whole system. I'm using CleanMyMac which clears some space, but the problem still persists. I've run Malware and virus scans and that's not showing anything up.

I've cleared over 200GB of files which hasn't done anything, and on Storage its showing I have 281.2 GB of free space.

System Details;

iMac (Retina 5K, 27-inch, 2017)

3.5 GHz Quad-Core Intel Core i5

48 GB 2400 MHz DDR4

Macintosh HD

Radeon Pro 575 4 GB

I've deleted caches countless times, tried to untick "Back Up Automatically" on Time Machine but for some reason it still stays checked.

I've tried repairing the disk in Disk Utility whilst in recovery mode twice, restarted and the repair doesn't show any issues or repair anything.

I really don't want to reinstall iOS, so hopefully someone else has had a similar problem and found a fix!