Sorry yes lol HiiT I have the Garmin Vivoactive 4S
You can find the list of watches supporting individual activity types in the following article. Vivoactive 4S does not support HIIT directly. You can still use a Connect IQ app, such as for example the "Any Activity" or "Any Sport" for assigning the HIIT type to your activities, or you can record it as Cardio, as you suggested in the OP, and then change the activity type to HIIT in Garmin Connect.
