Like the title says. In this example it says -16,3%.
IIRC, it is how much harder or easier the workout is comapred to what you have done recently, though I can’t recall the timeframe it compares to.
I am working on getting ChatGPT to answer these questions from all the support I have given. Here is what it says
The percentage amount on the “Today” tab represents the average intensity of your workouts over a certain period. For example, if your average intensity is 0.75, then a workout with a percentage figure above it would indicate that it is 16.7% less intense than your average.
It’s pretty close. But it’s not over your average it’s the average intensity of your harder workouts last week. It’s mostly just a confusing number but what you can see is as you press refresh it it goes from easier to harder (smaller negative) in generally but it’s also just approximate. But we attempt to make these workouts hard but not too hard.