Screens (and some functions) differ between iOS and Android EBC but Mode is on the main screen during indoor workouts.
Android: Quick Start Guide: EBC – Xert (baronbiosys.com)
iOS: Using The Xert App for iOS – Xert (baronbiosys.com)
I suggest you try EBC with a workout you are having issues with on your trainer.
You can quickly toggle through modes while the workout runs if necessary,
If you want to avoid that step you can also edit the workout in Workout Designer so that portions of the workout run in ERG mode while problem sections switch to Slope. Mode stays set to AUTO for the entirety of workout. Some workouts in the library already work this way (called mixed mode).
If you do need to edit a workout, view it in Workout Designer, click Copy button at bottom and when you save the workout “(Copy)” will be appended to the title. The workout is then available from your Personal folder and during filtered searches and included in XATA recommendations. You can also mark the workout as a favorite to make it available as a drag and drop entry in the Planner.
I believe the mixed mode Copy version would also work on the Garmin player.
Initially I did use my Garmin 1030 indoors, but now I much prefer EBC.