You can do workout in Road Grand Tours as well. Or you can manually add workouts to SYSTM calendar. If you have custom training plan built from Sufferfest workout library you have to manually search their library by workout name. Wahoo X (Wahoo SYSTM, former Sufferfest plus Wahoo RGT (Road Grand Tours)). What is shortest and easiest method to upload workouts? Do you still have to use Trainerday?
Download now is direct connection in Settings. If you have separate indoor and outdoor FTP values you can mark your workout as “indoor” and Intervals will use your indoor FTP. If you want to use your Garmin as smart trainer controller pair your device with trainer as FE-C trainer, then use workouts same was as outdoors. Connect Garmin in Settings, automatic download of completed exercises and upload of planned workouts.
If you use some service daily please correct me if necessary and I will update this post. It would be useful to create one topic listing how popular training apps send and receive data.