WebAssembly64 lets Unity Web builds grow the WebAssembly heap up to 16 GB by using the WebAssembly Memory64 extension. Although 64-bit pointers allow a much larger address space, Unity Web builds are currently limited to 16 GB by the WebAssembly JavaScript API specification.

Use WebAssembly64 only if your application requires more than 4 GB of memory. This feature can increase code size and runtime overhead.