Use your mobile browser to download a legacy APK from a trusted site like APKMirror .
Go to Settings > Security and check the box for "Unknown Sources" to allow installations from outside the Play Store.
You can find the latest compatible version on the official Facebook Lite page or Facebook Lite on APKMirror . Downloading Older Facebook APKs (Android 4.1+)
Loads faster and is optimized for low-RAM devices.