I'm running Windows 10 version 1909, OS build 18363.900.
After upgrading my Win 10 version, my HDD has been almost full, degrading performance. I now have about 40MB free on my 436 GB C:\ drive (my main partition).
System \ Storage says that I have 134 GB in "Temporary files", the same as the 134 GB in "Apps & features". (Before the upgrade, I had about 100 - 200 GB free.)
Opening "Temporary files" only shows 1-2 GB of files (which I do not want to delete).
Thus, it looks like "Temporary files" might be mirroring "Apps & features", but in a way that I can't disable/delete.
I've deleted C:\Windows.old. This initially gave me about 10 GB free, but it's filled up again. Disk Cleanup and malware scans don't find anything.
WinDirStat (suggested by @RamHound) shows a 10 GB C:$Recycle.bin with directories like S-1-5-... that I can't delete. It also shows an 132 GB C:\Windows\Temp<Files> directory containing .evtx files like Microsoft-Windows-Store_Operational_... which I can't even find in Windows Explorer, let alone delete. These two directories seem to be the problem.
