Setting a bool to 'true' on only the FIRST frame a button was pressed

What is the simplest way to get a bool to be “true” on the first frame of a button press, then back to false on the second frame of the a button press?

Is there a way to do this with the “new input system” ? It seems like it should be trivial, but all I can find are suggestions about using callbacks, and the “.started” attribute, and this does not work.

Depending on what you’re doing.

For Actions look for the triggered
https://docs.unity3d.com/Packages/com.unity.inputsystem@1.0/api/UnityEngine.InputSystem.InputAction.html#UnityEngine_InputSystem_InputAction_triggered

For Controls look for
https://docs.unity3d.com/Packages/com.unity.inputsystem@1.0/api/UnityEngine.InputSystem.Controls.ButtonControl.html?q=wasPressedThisFrame#UnityEngine_InputSystem_Controls_ButtonControl_wasPressedThisFrame

Also I guess you are somewhat familiar with the old input manager and looking for the same functionality despite this new better system, read through this:
https://docs.unity3d.com/Packages/com.unity.inputsystem@1.0/manual/Migration.html