When launching octave I get the following popup
then nothing in the Documentation tab
running Octave 4.4.1 on ubuntu 19.10
Can you please help
Can you display the Octave help via
assistant -collectionFile /usr/share/octave/4.4.1/doc/octave_interpreter.qch
or do you face errors? There was a similar bug  solved for Octave 5.1.0, when the help files are stored at some read-only location and indices cannot be written.