Bitumen coating despite finished exterior plaster

That already looks like a sealing material like Sockeldicht, for example, and not like a bitumen coating. However, I also think it will work. Pay attention to the details, so seal deep enough and apply it thick enough everywhere. Of course, this is not really professional or according to the textbook, but I often see thin plasters on the base without any sealing, where the damage occurs because no one thinks about it. Ideally, seal somewhat higher, as it is backfilled. The bitumen coating is, of course, not so ideal here due to its appearance. Noppenbahn and possibly insulation boards as described before are sensible, since the plaster can probably be damaged more easily (since it is not base plaster).