Lightroom isn’t the best tool for this cleanup before import. The community solutions point to doing it at the file-system level instead.

On Windows, a simple command-line approach is to loop through RAW files and delete the same-named JPG if it exists. For Nikon NEF files, one answer suggested:

for /f "delims==" %r in ('dir /b *.nef') do del "%~dpr%~nr.jpg" 2> nul

Add /s to the dir command if you want it to process subfolders too.

If you want something safer and more flexible, use a Python script instead. The shared scripts can:

• work recursively through subfolders
• match files only within the same folder
• handle case-insensitive extensions
• support multiple RAW extensions
• move JPGs to a backup/wastebasket folder instead of deleting immediately

That last option is the safest, since you can verify results before permanently removing anything. In short: use a script or command outside Lightroom, and ideally move the JPEGs first rather than deleting them outright.