The recent spike in Covid cases because of more dangerous variants, Disneyland has started requiring masks be warn indoors for all guests including those that have been vaccinated. The new indoor mask requirement also applies to everyone using Disneyland Resort transportation.
Unvaccinated guests are still required to wear masks in all locations although Disney employees are not checking vaccination status. The rules apply at the whole resort area including the Disneyland and California Adventure theme parks as well as Downtown Disney.
(Courtesy of Pirates and Mice.com)