The codec is installed, but hardware decoding is disabled. Solution: In Settings → Decoder, ensure all checkboxes under "HW+ decoder" are enabled. Disable "Use Software Audio Decoder" unless absolutely necessary.
: "Armv8 Neon" specifically targets newer 64-bit Android devices. If you are unsure of your processor type, the AIO (All-in-One) zip file is generally recommended as it includes all necessary variants. How to Install the Codec Mx Player 1.49.0 Armv8 Neon Codec Zip File