Created attachment 165588 [details]
Sample document to show the problem
When a document has Record Changes and Show Changes both enabled so as to track changes, if you clear direct formatting via CTRL-M, Writer does not register that any change has occurred.
See attached tiny sample document.
I confirm it with
Version: 184.108.40.206 (x64)
Build ID: 7cbcfc562f6eb6708b5ff7d7397325de9e764452
CPU threads: 4; OS: Windows 10.0 Build 19041; UI render: Skia/Raster; VCL: win
Locale: de-DE (de_DE); UI: en-GB