@Constantin-Marinescu Please go into the program settings and select an ASIO driver as your audio driver. Only if you select an ASIO driver you will be able to hear live input. Be also sure that your keyboard is selected as the MIDI input in case it is a MIDI keyboard (of course this does not apply if you play with your computer keyboard or on-screen-keyboard).

This is how I set it up on my laptop. I selected an ASIO driver (Magix Low Latency) and in the advanced settings I opened and activated all needed inputs and outputs of my Realtek audio chip which controlls audio of the speakers and headphones on my laptop. You need to select the audio device you are using.