If you can’t run XMB an alternative is to create a workout using the XMB Workout Generator, send that to your Garmin with the Send icon , then use Garmin’s native workout player during the ride.
First you need to launch the Workout Player App from a profile that has GPS enabled (e.g. not INDOOR), and then you need to enable GPS in the settings. GPS is disabled by default, as it was originally intended for indoor use. While we’ve arguably done an amazing job with the workout player app (2-time Garmin App of the Year), there are many limitations of trying to build an bike computer app within the confines of the ConnectIQ system.
Its likely better/simpler to just send the workout to Garmin & use their native workout interface (and allows for navigation, custom data fields, etc.) or install & use the Magic Buckets data field instead, as @ridgerider2 suggested above.