Hey eurban,

There are multiple ways to do so. If you open the application without IAM, you could use the Extended property: 'RibbonDisplay’ and set it to 'closed’. This way when you open the application the ribbon should be closed. 
(More info here: https://docs.thinkwisesoftware.com/docs/sf/extended_properties.html - RibbonDisplay)

The other way is via IAM where you can define an user preference for having the ribbon closed upon starting the application.

Hope this help!,

Kind regards,
Mark Jongeling