The KFX Input plugin does not remove DRM nor does it call the DeDRM plugin.
It does perform various non-DRM related manipulations of books in KFX format, such as combining the individual files that make up a KFX book into a single KFX-ZIP file and extraction of KFX metadata. Those functions are needed in order for calibre to be able to manipulate books in KFX format and so KFX Input must be installed along with DeDRM in order for KFX DRM removal to be successful.
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Amazon has been aggressive in updating the DRM associated with KFX format so that DRM removal only works in a few very specific situations involving outdated Kindle software. See the DRM Concerns section of the
KFX Input plugin documentation for details.
Beyond that, detailed assistance with DRM removal is not allowed here on MobileRead. If further help is needed then the best place to ask is in the Issues section of
noDRM's GitHub.