Hi,
You can always work with 3rd party LCD or components depending on the interface and your board. The STM32H747 eval/dk boards which are similar to the H757 eval, have DSI displays. So if you also want to use a MIPI DSI display you can use the TBS for the STM32H747 disco (the EVAL is not up to date yet) as source of inspiration for your configuration. I would recommend to start your project from STM32CubeMX instead of STM32CubeIDE if not too late. Within STM32CubeMX you will have to set whatever is necessary for your display, then in the TouchGFX Generator section set the display interface to whatever you have.
You can follow the Board Bring Up articles in the documentation to help you at first. You also have a couple of good videos made by ST and other users.
You can always continue your design with TouchGFX in parallel to your board setup by doing your GUI on the "simulator" (create a project with the simulator and a blank UI, make sure the width/height/bpp correspond to your setup). Once your board setup is finished you can use the "Import GUI" option to import your design to your project.
/Romain
