This vacuum cleaner MJSTG1 exists with both CN and Global versions available on the markets, hardware wise they seem to be the same, so difference is only in the firmware - I assume.
That being said, CN version - can connect only to China region in Mi Home App, most other devices I have are...
I have the same problem, no keyboard popping up.
EDIT: another problem is: when entering PIN i can barely see the button for confirmation,only the top part of it, it's cut off