The Strava mobile app doesn't support exporting activity files. You need to use the web version to download your activity file.
Log in to strava.com in your browser
Open your activity details
Tap the More menu (•••) on the left
Select "Export Original" to download your activity file
Tap "Open in RunCut" to start creating your video
A .fit.gz file is your original .FIT file compressed with gzip for faster transfer. RunCut recognizes and processes .fit.gz files natively without third-party unzipping tools.
Long-press the strava.com link in your browser and select "Open in New Tab" to bypass mobile app deep link redirection.