Workout builder

Yes.. you can. The workout will have Power (sent to the trainer, or just showing you on screen if workout is outside) and your target HR (be it, HR or LTHR)

Indoors - Smart Trainer - Power will be sent to the Trainer and you’re to follow/adhere to the HR yourself
Outdoors - everything will just be shown on the screen (bike computer) and you will just follow it

Data /workout will be sent to the bike computer and you just do the workout according to what’s shown on the screen.

If you’re looking for a way to execute workouts based on Power AND HR, you can take a look at this thread. The app will control your smart trainer such that you will follow your prescribed HR. (but take note that HR is a lag measure)