Ok, after a deeper research on the forum, I have seen the same question asked a few weeks ago, and already answered by David.
It seems it is by design. It is understandable because all graphics in the activity page are time based (all X axis are by time):
I asked for it because I can see the very same workout correctly matched on Garmin with the actual activity:
However, I cannot see a easy way to do it anyway in the current activity charts in intervals.icu.
So, perhaps I could convert this post in a small feature request: Is it possible to see the total distance in km of the workout programmed? Anyone else see this helpful?