The formatting of TOC entries is controlled by the TOC 1--TOC 9 styles. You can modify these styles, for example via References | Table of Contents | Insert Table of Contents | Modify.

Also, note that direct formatting applied to headings will reflect in the TOC. To fix that problem, select your headings and clear the direct formatting (Ctrl+SpaceBar). Then update the TOC.

__________________
Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional