GNU Octave version 4.2.x branch unfortunately contains a few GUI related regression bugs. Firstly, the menu options such as File, Options, Grid etc. can be hidden. A fix is incorporated into the current FEATool distribution, but please do report any errors by sending in a bug report.
Alternatively, Octave versions 4.0.0 through 4.0.3 can still be used as few new Octave features will improve FEATool functionality.
The second bug concerns Windows systems with HiDpi screens. In this case be aware that radio buttons and check boxes will be displayed very small. Unfortunately, there is currently no fix for this except for using an older version of Octave.