Chart titles and axis titles give Excel readers different kinds of context. Microsoft explains that axis titles are available for many axes, but some chart types do not support them. Pie and doughnut charts have no axes to title, while other specialized types have their own limits.

Add Only the Chart Titles Supported by the Visual

Select the chart and use its chart-element controls to add or remove a title. Choose a placement that does not obscure the plotted values. Check wording and formatting after resizing the visual so a title clarifies the measure and scope without colliding with the data.