So I dug a bit into it, it seems to me that the problem is in this section of aten/src/ATen/CMakeLists.txt, which by the way hasn’t evolved between 1.9.1 and current master:
if(BUILD_LITE_INTERPRETER)
  set(all_cpu_cpp ${generated_cpp} ${core_generated_cpp} ${cpu_kernel_cpp})
  append_filelist("jit_core_sources" all_cpu_cpp)
  append_filelist("aten_cpu_source_non_codegen_list" all_cpu_cpp)
  append_filelist("aten_native_source_non_codegen_list" all_cpu_cpp)
  list(APPEND all_cpu_cpp ${Aten_TH_AVX_extra_src})
else()
  set(
    all_cpu_cpp ${base_cpp} ${ATen_CORE_SRCS} ${native_cpp}
    ${native_ao_sparse_cpp} ${native_sparse_cpp}
    ${native_quantized_cpp} ${native_mkl_cpp} ${native_mkldnn_cpp}
    ${native_utils_cpp} ${native_xnnpack} ${generated_cpp} ${core_generated_cpp}
    ${ATen_CPU_SRCS} ${ATen_QUANTIZED_SRCS} ${ATen_NNAPI_SRCS} ${cpu_kernel_cpp}
  )
endif()

It seems that ATen_NNAPI_SRCS files are not included in the build when building the light interpreter. (They are actually built, I can find the .o files, but not linked into the output library)
We tried rebuild pytorch with this patch
diff --git a/aten/src/ATen/CMakeLists.txt b/aten/src/ATen/CMakeLists.txt
index baf9666f11..19f9a78443 100644
--- a/aten/src/ATen/CMakeLists.txt
+++ b/aten/src/ATen/CMakeLists.txt
@@ -130,7 +130,7 @@ add_subdirectory(quantized)
 add_subdirectory(nnapi)
 
 if(BUILD_LITE_INTERPRETER)
-  set(all_cpu_cpp ${generated_cpp} ${core_generated_cpp} ${cpu_kernel_cpp})
+  set(all_cpu_cpp ${generated_cpp} ${core_generated_cpp} ${ATen_NNAPI_SRCS} ${cpu_kernel_cpp})
   append_filelist("jit_core_sources" all_cpu_cpp)
   append_filelist("aten_cpu_source_non_codegen_list" all_cpu_cpp)
   append_filelist("aten_native_source_non_codegen_list" all_cpu_cpp)
diff --git a/scripts/build_android.sh b/scripts/build_android.sh
index daad46e8fb..211f5bb429 100755
--- a/scripts/build_android.sh
+++ b/scripts/build_android.sh
@@ -147,7 +147,11 @@ if [ "${ANDROID_DEBUG_SYMBOLS:-}" == '1' ]; then
 fi
 
 if [ -n "${USE_VULKAN}" ]; then
-  CMAKE_ARGS+=("-DUSE_VULKAN=ON")
+  CMAKE_ARGS+=("-DUSE_VULKAN=${USE_VULKAN}")
+fi
+
+if [ -n "${USE_NNAPI}" ]; then
+  CMAKE_ARGS+=("-DUSE_NNAPI=${USE_NNAPI}")
 fi
 
 # Use-specified CMake arguments go last to allow overridding defaults


diff --git a/aten/src/ATen/CMakeLists.txt b/aten/src/ATen/CMakeLists.txt
index baf9666f11..19f9a78443 100644
--- a/aten/src/ATen/CMakeLists.txt
+++ b/aten/src/ATen/CMakeLists.txt
@@ -130,7 +130,7 @@ add_subdirectory(quantized)
 add_subdirectory(nnapi)
 
 if(BUILD_LITE_INTERPRETER)
-  set(all_cpu_cpp ${generated_cpp} ${core_generated_cpp} ${cpu_kernel_cpp})
+  set(all_cpu_cpp ${generated_cpp} ${core_generated_cpp} ${ATen_NNAPI_SRCS} ${cpu_kernel_cpp})
   append_filelist("jit_core_sources" all_cpu_cpp)
   append_filelist("aten_cpu_source_non_codegen_list" all_cpu_cpp)
   append_filelist("aten_native_source_non_codegen_list" all_cpu_cpp)
diff --git a/scripts/build_android.sh b/scripts/build_android.sh
index 4dcb00becb..211f5bb429 100755
--- a/scripts/build_android.sh
+++ b/scripts/build_android.sh
@@ -150,6 +150,10 @@ if [ -n "${USE_VULKAN}" ]; then
   CMAKE_ARGS+=("-DUSE_VULKAN=${USE_VULKAN}")
 fi
 
+if [ -n "${USE_NNAPI}" ]; then
+  CMAKE_ARGS+=("-DUSE_NNAPI=${USE_NNAPI}")
+fi
+
 # Use-specified CMake arguments go last to allow overridding defaults
 CMAKE_ARGS+=($@)

And it works!!!. It requires launching build_android.sh with extra arguments USE_VULKAN=OFF USE_NNAPI=ON (unless one wants to activate Vulkan).
Note that ATen_NNAPI_SRCS is only defined when USE_NNAPI is on, so it makes sense to add the content of ATen_NNAPI_SRCS also in the lite scenario, because it will only increase the size of the resulting library if one explicitly requires NNAPI.