Is basement waterproofing available in the old building from 1971?

What should I find there? I think there is something black m, could that be a bitumen layer? That would then be a good seal and should be enough?

Black will probably be bitumen, yes. That is how it is done today as well.

Black is probably bitumen, yes. That's how it's done nowadays too.

Okay, but isn’t a dimpled membrane also applied nowadays? Is it sufficient without it? And should the waterproofing still be intact after 50 years? If you ever have to excavate the basement: we have the garage directly next to the house. You can’t really dig there, can you, or how is that done?

The bubble wrap serves as mechanical protection for the sealing, so that it is not damaged by sharp stones or other things. This is still done today – alternatively, relatively thin Styrodur boards.

50 years would at least be a period after which you should take a look at the sealing, but that does not necessarily mean it has to be leaky. Nevertheless, I would keep this in mind – when considering purchasing the described object. It is simply not a carefree new build.

If the basement below the garage becomes leaky, the only option would probably be to seal it from the inside. Google "Schleiervergelung."

Bubble wrap serves as mechanical protection for the sealing, so that it is not damaged by sharp stones or other things. This is still done today – alternatively, relatively thin Styrodur boards.

50 years would at least be a period after which you should take a look at the sealing, but that doesn’t necessarily mean it has to be leaking. Nevertheless, I would keep this in mind – if you are considering purchasing the described property. It’s simply not a carefree new build.

If the basement under the garage becomes leaky, then probably the only option is to seal from the inside. Google "Schleiervergelung".

Ok, and in case of doubt, could you just leave the basement damp if it is only used as a utility cellar?
And internal vs. external sealing? Roughly what costs are we talking about?
It is 12 x 6 meters, whereby one side adjoins the other semi-detached house.

Simply leaving the basement damp will likely lead to mold growth. In the past, basements were always damp, but they were naturally and continuously ventilated. That is usually not the case today, so that probably wouldn’t be a good idea. I can't say anything about the costs, but there are specialized companies in your area for that. You should ask them.