@AUGUSTO_MARTIN_FERNA You can not generate a new folder with Blocks using the present version of App Inventor. The File control cannot create a directory. Creating a directory is probably possible with Taifun's File extension at least for Androids lower than perhaps 11.
Once MIT releases nb187 (for sdk 30), creating a directory using the extension may no longer be possible. nb187 will introduce a new version of the MIT File component that may or may not be able to create a directory.
Things like this will start to be complex. It is difficult to explain all the changes until the dust settles and nb187 is released because changes are still in progress.