[DiapDealer]

On Windows:
Windows: C:/Users/<USER>AppData/Local/sigil-ebook/sigil/ IS the standard Sigil prefs folder. C:/Users/<USER>AppData/Local/sigil-ebook/sigil/cache/QtWebEngine exists (with cache data under 'Preview'), and it gets recreated when deleted and Sigil is relaunched.

There was also a QtWebEngine folder without the 'cache' prefix in the prefs folder (C:/Users/<USER>AppData/Local/sigil-ebook/sigil/QtWebEngine) but it does not get recreated after deleting. I fear older versions of Qt wrote to different locations).

There is also a 'QtWebEngine' folder under C:/Users/<USER>AppData/Roaming/sigil-ebook/sigil that contains an empty 'Preview' folder that gets recreated when deleted, but doesn't appear to have any actual cache data being written to it.

So on both Linux and Windows a 'Preview' cache folder is being created that doesn't appear to have any cache data being written to it. At least not always.