Thanks for reminding us about this issue. We currently have it tracked as part of Some widgets not updating appropriately on style change · Issue #5135 · Slicer/Slicer · GitHub. Toggling style may be a workaround for you to trigger an appropriate update for you to be able to read the label text. Edit → Application settings → Appearance → Style
xref: Parts of a module user interface are unreadable in dark mode on macOS