If one tries to enter some text with the default virtual keyboard on windows, Emojis that are composed of 2 16-Bit characters will not show.

Example:
The Emoji 😀 has the code "U+1F600" as ucs4 - and "U+D83D" + "U+DE00" if transformed to high/low surrogate. If entered via copy/paste, everything works fine, but if entered by the virtual keyboard, nothing happens.

I verified it's not the virtual keyboard, since applications like word, chrome, ... receive the character without problems.

Interesting enoug: It seems that the key-events are correctly delivered, but since each of the two characters is not displayable on it's own, they don't appear?
I installed an event filter to check the keys, and this is what I get for the emoji:

KEY:   55357 
 MOD:   QFlags<Qt::KeyboardModifiers>(NoModifier) 
 NVKEY: 231 
 NSCAN: 0 
 NMOD:  512 
 TEXT:  "\uD83D" (Size: 1 )
KEY:   55357 
 MOD:   QFlags<Qt::KeyboardModifiers>(NoModifier) 
 NVKEY: 231 
 NSCAN: 0 
 NMOD:  512 
 TEXT:  "\uDE00" (Size: 1 )

I attached the test project. To properly test you will have to use the "new" virtual keyboard. It can be activated by rigth-clicking the taskbar and selecting the option. Now you can access it by using the symbol in the taskbar.