WieWaldi Anybody an idea what virtual keyboard is capable of doing this?
I think you could likely do this with Keysight, it's pretty flexible/configurable (though no pedal visualization as far as I know). It's $29 USD on Steam for a perpetual license. It might have flashier illumination effects than you're after, but could be worth a look. At the very least, you can have the inactive keys and background black in Keysight, and configure the illumination however you want, and try something like an additive blend in OBS (or editing software like Davinci Resolve, etc.) to make the whole Keysight output invisible except for the active keys and overlay it on your keyboard camera.
There's a Discord server where the dev often helps folks figure out how to do all kinds of interesting things with it. He's also really responsive to feature requests (or at least he has been in the past). I think he's currently reworking the whole app architecture from the ground up in version 2.
This isn't the exact effect you had described, but like I said it's really configurable. Here's one possibility (you could just scrap all the flares, falling notes, etc, and use whatever texture you like on the keys):
Another example, since it's using a 3D model (of a Roland FP30, specifically) you can pick any angle you want and superimpose the Keysight visualisation on your real keybed. This one would look better with some anti-aliasing (and he has falling notes in it which I don't believe you wanted), but you get the gist:
