You will need to use a couple of filters and custom code to accomplish this.
First step, is to add a hidden field to the form that will allow you to capture the user ID of the user completing the User Input Step with the gravityflow_step_complete filter.
Second step, you could use either of the filters below to block or remove that user from the approval step:
Thanks for that, may need to dust off (de-rust) my PHP skills a bit to see if we can get this working.
I think the assignee filter may be a better fit as that way you could also achieve:
assign step to who completed the previous step
type scenario’s as well with roughly the same code.
I think if Gravityflow would support this natively, a lot of very powerful scenario’s become possible.