Wrong mapping on the onscreen keyboard (Ubuntu 20.04, default onscreen KB)

I have Ubuntu 20.04 desktop and I use the default onscreen keyboard. I have added a second language (greek) and it works fine on a real keyboard, but on the onscreen keyboard, some keys don't work (don't do anything) i.e. the backspace and the enter.
Do you know where can I find the onscreen key mapping and correct it?