German economic growth in the 20th century
$1.$ My guess is that your videographic's data were simply from the World Bank's GDP (current US\$). This is nominal GDP in US\$ and does not take into account (a) changes in the exchange rate; or (b) inflation.

$\color{red}{\text{2.}}$ And it turns out that the chief culprit here is (a). To correct for (a), we look instead at GDP (current LCU), where Germany's LCU = Local Currency Unit is the euro.

$\color{blue}{\text{3.}}$ We can also further correct for (b) by looking at GDP (constant LCU).





P.S. I would not trust the website VisualCapitalist.com. Here for example, it simply took this videographic from a tweet, which in turn gives no sources.