It's been +5 years since KDE5 Plasma was released and we still don't have X11 Cursor Thumbnails. Not everyone would care about this issue but the thumbnails come very handy when designing cursors or to learn what image does what according to the title on each .xmc file.

For now I use an alternative, but the alternative makes .xmc files turn into .png previews, thus making the icons blurry.