I know of 2 very common modulations that classical music composers of all ages have done. Those 2 are relative modulation and parallel modulation respectively. I myself have done those and I see both of these types of major/minor shifts in Beethoven's music all the time. Even his fifth symphony which for the first movement mostly stays in C minor, has both the parallel and relative major in it. But there are some other modulations that I hear in Beethoven all the time that I likely would not hear in Chopin, Mozart, or even Schubert, at least not often. The Pathetique Sonata is a good example of one of them.
Here is the modulation sequence of the Pathetique Sonata up to the development section:
Cm -> Eb -> Gm -> Em
That last one, the only way I could really describe it besides a direct modulation is modulating to the relative minor of the parallel major. It has both a relative modulation and parallel modulation but they occur simultaneously. The reason I hear it this way primarily has to do with all the B naturals at the end of the G minor section.
But there is one Beethoven piece which tops that in terms of the number of direct modulations and is even more famous. That of course being his ninth symphony. Just in the first movement alone there are shifts back and forth between these 4 keys:
- D minor
- F major
- Bb major
- C minor
D minor to F is very common. D minor to Bb is much less common. Even less commonly I hear Bb modulating to C minor directly and there are several moments in the symphony where there is a direct modulation between Bb major and C minor. And of course, in other movements there is modulation to D major as well. That is at least 4 different modulations, only 2 of which are expected modulations(the relative and parallel respectively).
Now I think the reason he is able to make all those direct modulations in his ninth symphony is because he is dealing with a large orchestra and modulations in an orchestra tend to sound smooth, almost as if they are expected, even when they aren't. Conversely, if I were to modulate from D minor to C minor and have it sound smooth, this is probably what I would do for a piano solo work:
D minor -> G minor -> C minor
Or have the melody change key while the harmony stays the same until I reach C minor at which point, I have the harmonic change occur. I have done that melodic change before and it works as long as you aren't modulating to a key that has an altered version of the original tonic. So this would work equally well for going to F# minor or even to A major. But it wouldn't work for Ab major or E major unless I had a second harmonic change, at which point I have covered every key in the circle of fifths.
But why is Beethoven able to make these surprising direct modulations in his piano sonatas and other works besides his symphonies and have it all sound as though it was expected?