Hey @Jarle_Tjessem welcome!
Sometimes the terminology we use here is a little well …stupid.
Your Homey actually has its ‘own apps’ which need to be installed upon it in order to add new devices.
Don’t worry its nice and simple, in this case as you are installing a fibaro device, you will need to install the fibaro app onto your homey.
Just head to https://apps.athom.com/app/com.fibaro - login and click the install button. Then when you click add button + you will have the option into pick the 'Fibaro" brand.
You will only need to install the Fibaro homey app once, and all fibaro devices are now supported. For other devices make sure you check out the ‘App store’.
Thanks and welcome
Click here for the support article.