Planting a 45° slope independently

Wow! I am currently facing the same problem (just reversed, I am lower), where the city is "dropping" a green strip about 0.5-1m higher than my land, and I had already firmly expected to have to install L-shaped stones there costing many thousands of euros... But now that I see your embankment... if it has held and worked like that for 16 years, then I no longer have any concerns about also grading it and "securing" it with proper vegetation.

That holds fast, however, we have very heavy clay soil and hardly any topsoil was dumped on the slope, most of it came from the excavation. But even with the poor soil quality, everything established itself quite quickly. In the first few years, we removed the worst wild growth between the shrubs once or twice a year. Since then, everything has just been growing on its own and I really only cut away the branches that grow too much. You also have to like it a bit wild, otherwise better something that can be "neatly" trimmed into shape.

The neighbor did it the same way, but he doesn't let the bushes grow as tall and trims more overall than we do.