before you say anything. Yes, this is a duplicate of https://support.papersapp.com/support/discussions/topics/30000001231
But, only because discussion has been closed in the other thread and the feature has not been implemented yet.
The last post even states that "you can set manual entries and if not, it'll use the DOI".
The point of autogenerating citekeys is that you can define a format like
<first author last name><year><first word of title>
and this is set as the default citekey, instead of having to manually set this for every single paper.
This feature does not exist yet! (I would be happy to be proven wrong, though)