By default the public cloud horizon interface will default to GRA1 datacenter. This will allow you to manage all your instances within this location. If you have other regions which you make use of, you can set the region default upon login on the URL.
This is the default URL:
https://horizon.cloud.ovh.net/auth/login/.
We can change this to:
https://horizon.cloud.ovh.net/auth/login/?next=/auth/switch_services_region/SBG1/%3Fnext%3D/project/