Originally Posted by Bob Ross

LOL! Here we go...

Regular readers of BF -- though admittedly more in the Road Cycling subforum than the 50+ -- are probably quite familiar with my take on this question. Call it my personal bugaboo. But for the record:

Your trainer/stationary bike covers no distance when you use it; it stays in one place (hence the name "stationary bike" ...the dictionary definition of Stationary is "not moving")
"Miles" is a measure of distance.
No distance = no miles.
Ergo, one literally cannot count any miles achieved on a trainer or stationary bike...because you did not achieve any miles.

However, you definitely A) spent some time on the trainer/stationary bike; B) expended some energy on the trainer/stationary bike; and C) caused the rear wheel to rotate on the trainer/stationary bike.
So, if you want to count something as an achievment on your trainer/stationary bike, count time, or work, or wheel revolutions.

Just don't count miles.

:::gets off soapbox:::