Currently, it is not possible to get power alerts on any Garmin watch. This is a limitation of the Garmin watch.
You can install the Stryd IQ Connect IQ on your Garmin watch to get a visual indication of your power zone.
Stryd PowerRace Connect IQ will allow you to set a power target and range. You will get a visual indication of whether you are within your range (green) or outside your range (red).
If you have additional questions, contact firstname.lastname@example.org.