A cancelled event usually shows up with the "[Cancelled]" label added to its title in the ics file, e.g.:
SUMMARY:Compute Accelerator Forum [Cancelled]
DTSTART:20230809T143000Z
URL:https://indico.cern.ch/event/1264299/
This also works fine when exporting/syncing an entire event category.
However, when using the Dashboard export/sync of "Your categories" the title appears unaltered:
SUMMARY:Compute Accelerator Forum
DTSTART:20230809T143000Z
URL:https://indico.cern.ch/event/1264299/