It’s not documented in the Cubase manual, like the the midi standard and the VST standard aren’t in there.
It’s discussed in the links above, especially the ROLI ones. Their synth does “support” it. But if you don’t have a controller that does this, it’s not of any use. You can do what you have always done, load a few instances of a VST into the plugin and use Note Expression to set channels and CCs/PB etc, of individual notes.
It’s the controller that has to support it, and it’s meaningless without such a controller. The whole point is that in MPE mode the controller automatically changes the channel for each note, and can be marketed as a miracle cure.
You know what synths support Note Expression, I’m sure this has been discussed here. It’s mainly Steinberg multi-timbral VSTs, and I think VSL.