Is there a keyboard shortcut for adding an entry to the index of an Libre Office Writer document? Using Insert - Table of Contents and Index - Index Entry is "unconvinient".
What keyboard shortcuts would you like to have for these operations? Look in Tools - Customize - Keyboard tab - there are a lot of keyboard shortcuts that are NOT ASSIGNED to any actions, choose any that seem comfortable to you.
Now in the Functions field write Table o - this is enough to see the Table of Contents command in the Function field. Highlight the desired keyboard shortcut, select the desired command (now it's easy, now it's one), click Modify.
Now in the Functions field write Index.
Assign a keyboard shortcut for each of the eight found commands (or just those you intend to use).
Now the hardest part is to remember these keyboard shortcuts and use them.