Create a new document and rename it directly (in one step) in Ubuntu 18.04
I've been looking for a permanent solution for this problem, and I found out that the best solution is to change the File Manager:
Nautilus is the default File Manager for Ubuntu. However, in Ubuntu 18.04 release, it does not allow creating and renaming files in just one step. So if anyone wants that feature to get back, the solution is to install another File Manager, I recommend Nemo (very close to nautilus in appearance) or Dolphin (more features). Both of them are available for install via ubuntu-software (or gnome-software).