I have never tried this before today, but in Garmin Connect Modern it gives the user the option to "Export Original" along with the TCX or GPX file. I assume by original it means the .fit file. But if I click that option, it tells me access is forbidden. Why? GPX and TCX exports work fine.
HTTP Status 403 - Forbidden
type Status report
message Forbidden
description Access to the specified resource (Forbidden) has been forbidden.
Apache Tomcat/7.0.28