In order to do this the reel must be uploaded to YouTube, and then handled the same as other videos.
Here’s some info from Google AI
AI Overview
To download your own Facebook Reels directly inside the mobile app, tap your profile picture, select your Reel, tap the three dots menu, and choose Download reel. To download reels made by other people, you must copy the video link and use an online video saver.
Downloading Your Own Reels
- Open the Facebook App on your phone.
- Tap your profile picture in the top or bottom corner.
- Find and tap on the Reels tab.
- Select the Reel you want to save.
- Tap the three dots (
...) or Options icon. - Tap Download reel to save it to your phone gallery.
Downloading Other People’s Reels
- Open the Reel you want to save.
- Tap the three dots (
...) or the share arrow icon. - Tap Copy link.
- Open a mobile web browser like Chrome or Safari.
- Go to a public extraction tool like FDOWN or FDownloader.
- Paste your copied link into the text box and press download.