What flow type should be used when called by Apex code?

The correct flow type to use when called by Apex code is an autolaunched flow. Autolaunched flows are designed to operate in the background without user interaction, making them ideal for use cases where a flow needs to be executed programmatically, such as when invoked through Apex.

By using an autolaunched flow, developers can encapsulate complex business logic that can be executed via triggers, buttons, or Apex classes without requiring a user interface. This design supports a seamless integration with Apex, as it allows for passing input variables to the flow and receiving output variables back into the Apex context.

Screen flows, on the other hand, are intended for direct user interaction and present screens for data entry. They cannot be invoked directly from Apex code due to their dependency on user input.

Platform-event triggered flows are designed to respond to platform events and are implemented primarily for event-driven architectures, not for direct invocation through Apex.

Scheduled flows are intended to run at specific times, like cron jobs, and are not suitable for on-demand execution by Apex code.

Overall, the autolaunched flow is the most fitting choice for scenarios where you need to call a flow directly from Apex, embedding business processes without the necessity for user engagement.