Remove all downloads from iTunes? (But keep them in iCloud)
In iTunes 12.6, under Music, select Songs and sort by iCloud Status. If that column is missing, right-click the column headers and tick iCloud Status.



Select all songs with a status of Apple Music by clicking the first one, holding ⇧ shift, and selecting the last one. Then right-click and select Remove Download. Repeat for all songs with a status of Matched, Uploaded and Purchased.



In fact you can simply select the first song with a status of Matched, hold ⇧ shift, then select the last song with a status of Uploaded. This is true in particular if you use iTunes Match rather than MUSIC.

The songs you want to leave on disk are marked as Duplicate and Ineligible.