I have a JetBlack Z1 Fluid trainer. It is not a "smart" trainer, but nevertheless, has a documented power curve. I also have a speed and cadence sensor on my bike that are connected to my Fenix 5.
On apps like Rouvy, Zwift, etc you can specify the trainer make and model and the app then knows the power curve of the trainer based on speed and can track your power output.
Does anyone know if Garmin supports this?