Gate the whole feature
FilamentUser and HasTenants. The method name is canUseFlexSearch, not a method from another search plugin.
Or configure the feature gate directly:
Gate a resource or page
canAccess() on pages, canGloballySearch() / canViewAny() on resources or record policies.
Source and command gates
CallbackSearchSource::authorize() is a feature gate; it cannot infer tenant constraints for an arbitrary external service or custom SQL query.