Quick URL you are using defaults to the default namespace and may not work directly for users in non-default namespaces. Users in non-default namespaces must be created and authenticated using federated Single Sign-On (SSO) configured with your identity provider (IdP) via IAM federation.
Please refer to the following documentations this might be helpful for you.
if i understand verry well, it is impossible to have users in diffrent namespace authenticate to quicksight directly with url, an SSO configuration is mandatory for them right?
I wonder if it is the only way for them to access quicksight except iam identity center or active directory?
Yes, users in non-default (custom) namespaces cannot authenticate directly via the standard URL using password based login, federated Single Sign On (SSO) via IAM is mandatory for them. Custom namespaces support only IAM federated SSO users.
Yes, external OIDC IdP can be used to federate Quick users into different custom namespaces, as supports custom OIDC providers through IAM identity federation.
Please refer to the following documentations and videos this might be helpful for you.