Hanging with French Cleat or keyholes ?

Hi all, I'm making this bookshelf, dimensions are 100 cm wide, 87 cm high and 23 cm depth.
I believe it would be around 20 kilograms or a bit more, plus books. So I wonder how should I hang it to a concrete wall: 60 cm french cleat in the top board or a series of 6 - 8 keyholes in the vertical boards. At this point I'm only worried about it being sturdy enough for the book. thanks!

https://preview.redd.it/2uvh9n6sqvbh1.png?width=776&format=png&auto=webp&s=755d594172c99928e5284ec6a8f77ff02b64c9af