From The Document Foundation Wiki
How do I display a table of contents where the levels of title display only their own numbering and not the one from the higher level?
This type of table of contents, named hierarchical, is obtained by configuring the outline numbering:
- select the menu ▸ ▸ ;
- for each level, set Show sublevels option to 1;
- click OK; and
- update the table of contents to show the changes.