Please describe more in detail how you set up protection/restriction and what users can and cannot do. What are the specific symptoms? What goes wrong?

Generally, with document protection/restriction, users should be unable to use other styles than the ones you have allowed for them. (But do note that protection isn't foolproof. It can be circumvented rather easily if you know how.)

__________________
Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional