On most devices, while playing content, select Audio & Subtitles . “English 5.1” = surround mix. “English Original” = stereo mix. Some titles also offer “English Atmos” (object-based).
However, it's crucial to note that not all content on Netflix is available in 5.1. The availability of 5.1 audio depends on several factors, including: netflix 5.1 audio vs original