taking a look to the reference guide (e.g. ROOT: TMath Namespace Reference) many of the links to particular methods are missing (the black bold entries are without link):
These methods have no “More…” help, or just a brief which fits just below the method signature. There is no need for and extra link which does not provide any extra information. Only the methods having extra information (long description) have an extra link giving more details. (new feature of doxygen 1.9.2)