Where are Engine Preview Setting stored?

We can select a render preview mode in the editor.
Where is this configuration stored?

I changed a project to iOS preview and it crashed, now I am unable to open it anymore. removing all saved folders does not seem to affect this setting so it seems this is being stored at engine or user level somewhere.
I confirmed this with an empty project where the iOS preview does not go away even after removing the config, intermediate and saved folder.