The last major version of the full Facebook app to officially support Android 4.4+ was released around October 2020 (e.g., version 293.0.0.43.120).
If you're having trouble installing the regular Facebook app, consider using Facebook Lite, a lightweight version of the app designed for older Android devices and slower internet connections. Facebook Lite is available on the Google Play Store and can be installed on devices running Android 4.4.4 or higher. Facebook Apk For Android 4.4.4