In addition to deleting CAD Imports that you find using Ideate Explorer, you may also need to purge the symbol imports using Revit's Purged Unused tool.
Keep in mind, that Ideate Explorer can't look into individual families from the project environment to search for nested CAD Imports & Symbols. CAD Imports will still show in the Visibility Graphics Dialog under the Imported Categories then Imports in Families list if CAD Imports are being used in families within the project. You can use Ideate Explorer to look into each family when you open and edit the family to review if that specific family contains CAD imports. Good possibilities to start an investigation are Title Block and Generic Model families. These can typically contain CAD Imports.
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