How could i avoid singletons in this case?

using Dart in the client part of a web app where i have an application manager that contains a List of application instances and references to services that are used by each application as in the following diagram

as you can see the application manager is a singleton, so are the services that it contains which are used by all apps, to me it makes sense because

• i need to have only one instance of the ApplicationManager and each service


• easier to access services without the need to pass references


• i need to preserve the state of each service


• almost all services have a cache

i found ways to avoid having the services as singletons which is by making them private to the library which is a feature in dart, so i initialize the services only once from the application manager, but i can't make the ApplicationsManager private because its at the top most level of the library, i would appreciate your thoughts for a way to avoid having the application manager as a singelton