Problem solved: thanks to Tim Cusick at Velocious Cycling and Lauren at Zwift for their help.
So it seems some of the “workouts” you might get in a purchased training plan on Training Peaks aren’t actually workouts but performance “tests”. These tests, by their nature, can’t have the targets filled in ahead of time and thus Zwift can’t use them as a “structured workout”.
To explain, see the two images below. The one labeled “VO2max test” doesn’t have any data in the “planned” fields nor does it have any bars for the “warm up”, “Main Set” or “cool down” sections. Zwift will not show this “workout”. Per the folks at TP, you hit “just ride” in Zwift and follow the written test instructions as best you can for that day’s workout. TP should record the data (assuming you’re apps are connected) for that ride into the test protocol.
For the screed shot labeled “Progressive Endurance Ride” you’ll see the necessary fields all have data. Zwift will recognize this as a structured workout that will appear and you can follow.
Phew…