But I just found out that this option is also available in the plugin via the keycommands, so that's definitely a step forward now :-)

That sounds like a start, good luck with the video-ing - issues with fitting things onto screen can be tricky.

Unfortunately the interface magnification alone doesn't help because in ManyCam the PianoTeq interface has to fit as a whole.
What helps is the option of the "compact interface" what makes it less high. First I found this option of the "compact interface" by accident while clicking around in the standalone app interface. But I didn't remember where it is hidden.

But I just found out that this option is also available in the plugin via the keycommands, so that's definitely a step forward now :-)

When I'm in my DAWs using Pianoteq as a plugin, each DAW has slightly different ways to "show" the plugin.. but once Pianoteq is visible, it usually looks exactly the same as standalone (bar the menu). You def should see the keys animate.

And you should also be able to make the interface big.

Trick:

I do find tho, I need to first "click" somewhere on the Pianoteq plugin interface (on a part like where "C. Bechstein" or other piano name is painted).

Next, I use the + or - sign on the number pad.

For me, I find using the normal shift and + on the regular keys doesn't work for this.

But the key thing is to click the interface each time you then press the + or - on the numpad. Repeat to resize.

That's similar with a lot of plugins I find. After you do some specific thing, I find my 'cursor' back in the track.

In my case PianoTeq acts as a sound source, but I also want to display the piano keys view which can show the pressed keys and the chords.

In the standalone app there is a "compact view" wich helps a little to incorporate the piano keys view, but most of the time I use the Pianoteq VST in Dorico and here the compact view isn't available, at least I didn't find it. The result is that the display of the piano keys in ManyCam is very tiny.

The best would be to have the keys and chord display in a separate window or rather hide everything else.

I know that there are dedicated apps for displaying pressed keys and chords but it's already there in PianoTeq, so I am asking if it would be possible to implement this UI view option.