Does cum laude mean the end of an academic career in Germany
Well, yes, but also no.
Permanent academic positions that are not professorships are relatively rare in Germany. Since most researchers want to eventually have a permanent position, it is in the interest of all long-term researchers to eventually become &quot;berufungsfähig&quot; (suitable for becoming a tenured associate or full professor).
The vast majority of the universities are public in Germany, and hence the laws of the respective state regulate hiring in the universities. All(?) &quot;Landeshochschulgesetze&quot; (law on higher education) list mandatory requirements for candidates for professor positions.
For instance, the respective law of the state of North-Rhine Westfalia (that has the largest population) states as a requirement:

besondere Befähigung zu wissenschaftlicher Arbeit, die in der Regel durch die Qualität einer Promotion nachgewiesen wird;

In English, this means that the candidate must show a substantial/remarkable/special ability to research work, which is normally indicated by the quality of the PhD. Given that PhDs are thesis-only in Germany (while the defense may also include more general questions about the field of work), this means that the PhD thesis should be particularly good and have a corresponding grade. The state of Lower Saxony has in their law that the PhD should be above average, and given that there are four passing grades, &quot;cum laude&quot; is probably below average.
Now what does should mean concretely? It means that if a hiring committee wants to hire somebody with a bad PhD thesis, they risk the overall hiring process being delayed or even canceled. There may be objections, candidates not snatching the precious professorship may sue, or the respective ministry of education may intervene or simply refuse to send the offer letter to the successful candidate. There have surely been cases of pea counting as far as the formalities of candidates to be hired are concerned in the past, and this adds to the risk. Hiring committees and universities will probably take the risk if there is a very good and demonstratable reason for why the candidate is excellent despite a bad PhD thesis, depending on their legal interpretation of the should and how much they are willing to risk it. In any case, certainly, those candidates with a good PhD thesis have a substantial head-start, and it's quite hard to catch up for candidates with a grade lower than &quot;Magna Cum Laude&quot;.
Having said this, there are also other permanent academic positions, such as in Fraunhofer or Max Planck institutes that may or may not have similar requirement. So a Cum Laude may not be a big deal if they want you for a different reason.