The new OAuth2 Node Account Provider text field in the UI doesn't populate the default implementation class neither mentions it in the help text:
Default implementation is org.forgerock.openam.authentication.modules.common.mapping.DefaultAccountProvider. The org.forgerock.openam.authentication.modules.common.mapping.AccountProvider is the interface that the default implementation extends.
The Account Mapper help text does include the possible implementation classes. This can be confusing for customers.
In contrast, the Legacy OAuth2/OIDC module does pre-populate it: