Are the indents on projects limited to 2 levels? Is it possible to get more

I have developed a Gantt chart with a dozen main goals. I have broken each goal into 6-15 subgoals, showing them on my chart as indents under the main goal. I would like to add a second level of sub- subgoals. I am not able to do this. The right click menu shows the indent action as shaded out and when I click on it nothing happens. The outdent, up, and down actions are all available.

What options do I have?

There is no restriction on the number of levels, but there may be other reasons why one task can’t be a child of another, regardless of the level. The simplest case is when they are in predecessor-successor relationship, but other cases are possible too. Please share the project file if you are not sure what exactly is the case.