Hello @Emanuele78 ,
Once you have created you desired GUI, simply click on "Generate code" on the bottom right corner:

Then you can simply open the folder of your project on the bottom left:

Finally, open your STM32CubeIDE project in the STM32CubeIDE project.
Also, you can look at this video : How to TouchGFX: Creating my first GUI with TouchGFX Designer for STM32 GUI applications
Hope this help! :smiling_face_with_smiling_eyes:
If this answers your question, I invite you to select this comment as "best answer".
Regards,