Strava can show running power but only if the source is Polar, Suunto, Apple watch (using the Stryd app), and offline sync.
Users that have a Garmin watch cannot get power in Strava if the data is recorded by the watch and passed on to Strava (even if passed through the Stryd platform first).
This is due to the format of the Garmin FIT file. The only known workaround is to stop importing data from Garmin into the Stryd platform and upload the data from Stryd with the Stryd app on your phone to PowerCenter and then export the data to Strava (not recommended as you will get extra time added to your run and you will miss HR and GPS map)
If you need additional assistance, contact firstname.lastname@example.org.