Build a matter sample light bulb of SDK 2.6.1 for nrf5340DK.

Question

Hi, 
 One question, in VS code, 
 when I choose the nrf5340dk_nrf5340_cpuapp for build configuration, the VSCode told me the nrf5340dk_nrf5340_cpuapp is without security, 
 
 In Working with nRF5340 DK , 
 
 the link said, the "cpuapp" is for the secure, and "cpuapp_ns" is for the non-secure domain. 
 Which one is for the non-secure? 
 
 If I use " nrf5340dk_nrf5340_cupapp_ns " to build the light bulb sample, it appears the error: 
 (It is no problem if I use the "nrf5340dk_nrf5340_cpuapp" to build the sample.) 
 CMake Error at C:/ncs/v2.6.1/nrf/lib/fprotect/CMakeLists.txt:15 (message): No fprotect backend selected. 
 
 Please help to fix the error. 
 
 Best regards, 
 Aaron Deng