Dashboard blocks can be configured to show course short names using:

Site Admin -> Appearance -> Courses -> Display extended course names

The description of this setting hint about further customisability of showing course short names using the 'courseextendednamedisplay' language string.

The dashboard blocks do not support using this language string since the positioning on aa truncated separate line and .text-muted classes used in dashboard blocks to show the course short name should not be added to language strings.