Fix is available in version 13.1 of InDesign.
Please update to the latest version available to you via Creative Cloud Desktop application.
Adobe InDesign teamReno Gabriel Meier commented
In previous versions of InDesign, layers set to non-printing used to be shown in italic so it was clear right away that everything on this layer won't print. It seems like this feature has been removed in the latest update (Adobe InDesign CC 2018, V13) – could you please bring it back?
Thanks for the feedback. Moving this into our backlog.