While I don't think we know exactly when GP moved to Florida, according to this article it was in Jan 2019.
Gabby Petito lived, worked in North Carolina for more than 1 year prior to moving to Florida
She would have been about to turn 20 in Jan 2019. So she would have had a vertical "under 21" license issued in FL.
I know some folks think the Moab police made errors. But I really do not think they would have let her drive off by herself if she only had a learner's permit. And I think that's especially true given she expressed concerns to the officer about driving the van.
I'm pretty sure she had a license and I'm also pretty sure you cannot lease a car with only a learner's permit. But remember she didn't lease the Nissan. Her parents said they did. It may be they bought the van too. We don't really know except that evidence from the traffic stop suggests it was registered in her name. And her father was quite emphatic that it was her car....perhaps because he bought it for her.
JMO