When creating a 'Mobile Qt Application' I can only choose 'Harmattan' and 'Maemo' on the target setup page.

After creation of the project, it is possible to switch to the 'Projects' view and add 'Qt Simulator' to the list of targets.

You should either remove it from 'Projects' view's target selector - or add it on the target setup page...

(I have configured Qt Versions and Toolchains for all of the above mentioned targets before trying to create the project)