The last official version of YouTube to support Android 4.4 (API 19) was released in late 2019. You can find these legacy versions on trusted third-party repositories:
YouTube Android 4.4
Even with these APKs, you may experience network errors or broken video playback because YouTube's backend APIs have changed. Best Alternatives for Smooth Playback youtube android 4.4 4 apk download
While the official YouTube app has largely phased out support for older operating systems, you can still find the compatible and alternative ways to stream videos on your legacy device. Current Status of YouTube on Android 4.4.4 The last official version of YouTube to support Android 4
You're looking for information on downloading the YouTube Android 4.4.4 APK. youtube android 4.4 4 apk download