Use Safari and the FDown.net tool, or the Friendly Social Browser app to save videos directly to your Photos or Files app. To help you get the best result, let me know:
Replace www in the address bar with mbasic (e.g., changing https://www.facebook.com/... to https://mbasic.facebook.com/... ). Download Facebook mp4
Are you using a or a mobile device (iPhone/Android)? Is this a public post or a private group video? I can provide the quickest method based on your setup. How to Download a Facebook video for Free - Quick Guide Use Safari and the FDown