How to implement on screen keyboard with Compose?

Not sure what you are trying to do here? You want to write your own keyboard?

Implement a screen like this.

Ok. That is just a column of rows of circular buttons.

Yes, but how to perform key press event?

every button has a click listener which you can react to

I was expecting APIs like InputConnection, but I didn't find any.

@Alan Yin have you gotten a plain old button working? If you get a plain old button working then implementing a dialier like above should be trivial.

You can also look at the implementation of Button for clues about how to write your own