Does not show all RAM

Given that you have a mobile processor with built-in graphics (as can be seen from the CPU identification), these ~4 GiB are probably assigned to the iGPU. That's normal behaviour of these chips, and can maybe - depending on the motherboard/firmware - be altered in the BIOS/UEFI.
 
Given that you have a mobile processor with built-in graphics (as can be seen from the CPU identification), these ~4 GiB are probably assigned to the iGPU. That's normal behaviour of these chips, and can maybe - depending on the motherboard/firmware - be altered in the BIOS/UEFI.
And sure, I didn't think about it. Thank you