On 15.6.1. Expect this applies to other New UX versions, too:
This is standard behavior, regarding the difference between Fast and Power plans. I haven't seen much documentation on these play types since the ABT days:
In New UX, because one must use a template to create a project, to replicate the Fast Plan capability, one needs to have a template with no tasks/no WBS, no roles, not staff. Create the new project in the New UX with this empty template, than start adding staff/roles and the "Effort" Task will be created, just like in Classic view.
Q: I did it wrong – can I convert my project from one type to the other?