It can be quite hard to pinpoint exactly when serfdom stopped in Germany partly because Germany wasn't one but several different states prior to 1871, and secondly subtle differences in the exact definition of serfdom can change hugely when exactly it was abolished.

Serfdom can best be described as peasants being forced to work the land of their aristocracy. So this definition includes two parts a) there's a local Lord and B) that the lord is using force to have someone work.

The thing is what exactly 'force' is is a fairly open question. Obviously a Lord riding in on horse back and demanding that a given person farms his land on pain of death is force. But there's also more vague forms of coercion which can be considered force. E.g. the administration (Verwaltung) refusing to process paperwork to facilitate a peasant moving from one place to another. The existence of mere economic forces existed up until Bismarck introduced social welfare in the 1880s, where as the more strict definition of 'force' was abolitioned much earlier (although exactly how early is impossible to say due to the fractured stage of German politics pre 1871).

Even what nobility was can be difficult to establish. German nobles would continue to have titles (e.g. 'Von', which is one of the lowest noble ranks) until the present day (although the number of title holders is hugely reduced). And elite families would continue to wield power until at least the inter-war Weimar Republic (the Junker social class is well reported on for causing Weimar Germany difficulties).Germany would continue to have a Kaiser/Emporer/'Caesar' until 1919. Even the current German defence ministrt -Ursula Von Der Leyen - has a 'Von' in her name, suggesting nobility.

But of course the number of titles and the power starkly diminished over time. The Kaiser of 1871 was much less feudal than the one in 1700 (Friedrich I).

The earliest point that most historians would point to where the unravelling of feudalism began to take place was during and after the French occupation by Napoleon 1790-1815. Again it cannot be stressed enough that this occupation didn't effect the different parts of Germany equally. Some of the border zones of Germany with France were directly incorporated into French terrortory (and had cultural similarities with France going back even before 1790) whilst other regions were only briefly conquored/surrendered and then left largely unaffected. But generally it can be said that the French occupation helped kick started the over throwal of the nobility, aid in the introduction of meritocracy en masse (as opposed to only in small sectors like Prussian civil services & and the clergy as had been the case before).

Obviously setting the date of the end of serfdom as 1815 is too early, but setting it as 1880s (when Bismarck's welfare policies were introduced) also feels too late. The real answer is that serfdom disappeared (more or less) within this period but due to the ambiguity of the word serfdom and the balkanised nature of Germany in this period it's impossible to pin down an exact date. And I think that's actually a good thing. It forces us to consider really what it is like to be trapped in certain economic circumstances and imagine what it must have been like, which simply labelling something as 'serfdom' or 'not serfdom' doesn't provide.