An interesting landscape design solution: retaining wall for separating the patio area. It is difficult to determine from the photograph whether the height difference is used here or the wall has a purely decorative value. But it certainly looks beautiful and original.
The simplest option possible is presented: retaining wall of vertical logs. They are buried in the ground to a depth of about half a meter and fitted close to each other. Their diameter, following the advice of experts, should not exceed 18 centimeters, but using thinner than 12 is also not recommended.
So that the logs dug into the ground do not rot, they are recommended to be lubricated with machine oil or bitumen. This will protect them from moisture and extend the life of the wall.