The Ussuri release of horizon has the following dependencies.
Python 3.6 or 3.7
Django 3.2 support is experimental as of Xena release. (Yoga release will use Django 3.2 as the primary Django version.)
Django support policy is documented at Django support.
An accessible keystone endpoint
All other services are optional. Horizon supports the following services as of the Stein release. If the keystone endpoint for a service is configured, horizon detects it and enables its support automatically.