Painting old brickwork in the garden

In our garden, on a property boundary, we have an old brick wall (not a building wall), presumably from the 60s (see photo). Unfortunately, I don’t know if it is just bricks or if it is also faced with clinker bricks. Maybe someone can identify this look? In any case, the wall is continuously exposed to the weather and is now supposed to be painted gray because its color is dreadful. Can you give us a tip on how and with which products we should proceed in order to have a long-lasting paint finish? On the internet, one sometimes reads that "normal paint" probably will not adhere well to such clinker bricks. We are grateful for any tips!