VO2 Max ratings are incorrect on the vivosmart HR for age categories according to all other medical charts.

I think you might have misunderstood your cardiologist, or perhaps didn't ask the right questions. A cardiac stress test can be useful for diagnosing or ruling out certain medical conditions, however it isn't really intended as a fitness test. If you want to know your actual VO2 Max then you'll have to visit a sports medicine lab and run on a treadmill or pedal a stationary bike while wearing a breathing mask so that they can directly measure your oxygen consumption.

There is nothing "false" about Garmin rating a VO2 Max of 26 as Poor. The hard reality is that regardless of what you might see on some chart, that level of fitness leaves you with little reserve capacity and puts you at risk of no longer being able to live independently.

But again, the Garmin VO2 Max calculations are only going to be accurate if you feed the algorithm with enough high quality data. That means doing numerous runs at a variety of effort levels, including some at like 9/10 RPE. If you have only done lower intensity runs with your watch then the VO2 Max estimate may be way off. (Consult with a physician before starting high intensity exercise if you're not already accustomed to it.)

www.garmin.com/.../