NACL Web Plug-in is a legacy software component based on Google's Native Client (NaCl)

Tied to specific hardware (x86, ARM); required different binaries for different CPUs.

One significant limitation of the original NaCl was architecture dependence. A NaCl module compiled for an x86 processor would not run on an ARM device (like a smartphone).

Maintaining a secure native sandbox across multiple hardware architectures proved to be a massive engineering challenge. Current Status and End of Life Google officially began deprecating NaCl in 2017. Overview - Samsung Developer