How to divide a cell in a libreoffice?
If you expect any answer at all, edit your question to provide more information. Generic data: OS name, LO versions. Specific data: you tagged writer i.e. the text document application. Confirm this choice that you didn’t mean calc, the spreadsheet application where cells are the primary objects.
Read these guidelines.
Add a description of what you’d like to achieve.
Also, what do you mean under divide? Making several new cells from a single one? Then it is not divide but split in the LO Writer terminology, see Earnest Al’s answer. Or something else?
…and be aware of the fact that text tables with split or merged cells no longer are simple. If anybody at any time in the future might need to work with such tables by means of document automation (user code) aggravations will be substantial, There may no longer be a usable DataArray e.g. or none ata all in some cases. The situation is even much worse than in spreadsheets with merged areas.
(Splitting and merging is evil.)