Yandex is a Russian search engine which also provides personal services like email, address books and calendars.
If you have a @yandex.ru account, choose "Login with email address" and enter your Yandex email address and your password.
If you're using Yandex with a custom domain, choose "Login with URL/user name":
Base URL: https://yandex.ru
User name: your Yandex email address (firstname.lastname@example.org)
Password: your generated app password (when app passwords are active for your account) or your Yandex password
Contact group method: groups are per-contact categories
Only the group "Phone contacts" in the Yandex address book will be used for CardDAV (i.e. be synchronized with DAVdroid)! You can assign contacts to other groups and "Phone contacts".