No, an official English dub does not exist, so there is no "English audio track" to download. You can, however, download the original German audio track in high quality from the DVD or a digital purchase.
Platforms like Amazon Prime Video, Apple TV, or Google Play often offer the film with both original German audio (with subtitles) and an English dubbed version.
Most official releases of Downfall do include an English dubbed audio track. The filmmakers and critics generally agree that an English dub would diminish the raw, authentic performances—especially that of Bruno Ganz .