The keyboard handling is done by MSFS entirely outside our control, we just ask for a key, and the sim will simply call us back asking to do something if the key has been pressed. That's how Simconnect works so, if the simulator itself doesn't allow auto-repeat for key events sent back to a Simconnect app, there's nothing we can do from the app itself to prevent this.
That's why, in P3D, we got auto-repeat "for free", without doing any extra coding, because Simconnect there behaves differently, and it *does* auto-repeats calls when we ask for a key.
The only possible theoretical way to fix this ( other than MS/Asobo fixing or maybe adding some kind of flag to ask for auto-repeat ) would be making a very dangerous and invasive procedure called "global hook", that is intercepting keys on the whole Windows messaging queue, something that audio chat product usually do, for example to let you take a call by pushing a button on headphone even when you are inside another program. This method is so invasive, that most antivirus flags it as dangerous, unless you are in a special whitelist of popular apps, like Skype, Discord, Teamviewer, etc. this assuming the Microsoft own security on MSFS wouldn't block it anyway, because it's usually assumed to be a technique used when cheating in games.
So, we must work with what we have, to make a clean and safe and compliant Simconnect app.