If I understand you correctly, you’re trying to “open” the files created by saving, and expecting it to play back the flight?
That feature is for saving your current position in the flight so you can load and continue later. You can only open it in MSFS. I haven’t used it.
Edit: Actually it appears you’re talking about the flight plan. That saves/loads the flight plan.
If you’re looking to “record” your flight to playback later you can use this freeware tool, or one of the payware tools available.