I have both Windows Store and Steam version of MSFS installed.
When I click "Export Flightplan" button in iniManager, it will generate FMS file into the folder of Store version and no such file in Steam version. e.g.: fpl file only in Packages\Official\OneStore\microsoft-aircraft-a310-300\Data\FMS plans
Suggestion: If both versions detected, generate fpl file into both versions' folders.