Power BI Pro / Azure Databricks Standard Tier (LEGACY HIVE METASTORE) CONNECTIVITY

I AM GOING INSANE. For over 6+ years everything has worked perfectly.

I have an Azure Databricks setup that I connect to from Power BI Desktop using the Databricks host URL and HTTP path. I authenticate with either Azure Databricks token or OAuth/AAD, and Desktop connects without problems. I build the report, publish it to Power BI Service, and that part also works.

The problem starts in Power BI Online / Power BI Service.

I can no longer get the Power BI online platform to successfully connect to the Azure Databricks source in a reliable way, and I am trying to understand whether this is:

1. an authentication problem,
2. a connector issue in Power BI Service,
3. or some incompatibility between my legacy Databricks setup and the newer Power BI online connection flow.

Important details:

* I am using an organizational account.
* I do not have Premium capacity.
* My Databricks data is in a legacy `hive_metastore`.
* My Databricks cluster access mode is single-user, and that single user is me / the same account being used.
* Everything works in Power BI Desktop.
* Publishing from Desktop also works.
* The failure is specifically when trying to connect/manage credentials/create connections in Power BI Service / Power BI Online.

My Databricks connection info comes directly from the cluster (Host / HTTP Path)

In Power BI Service, under Manage connections and gateways, I have/had a working Azure Databricks connection using that host and HTTP path.

Errors I have received trying different things:

1. When trying AAD authentication:
“Unable to update connection credentials. We could not access the data source. Please make sure you have permission to access the data source and that your credentials are correct.”

2. When enabling “Single sign-on (use SSO via AAD for DirectQuery queries)”:
`AADSTS70008: The provided authorization code or refresh token has expired due to inactivity. Send a new interactive authorization request for this user and resource.`

3. When trying to create a brand-new Azure Databricks connection in Power BI Online:
`DataSource.Error: ADBC: Required parameter 'adbc.spark.host' or 'uri' is missing or invalid. Please provide a valid hostname or URI for the data source.`

This is the part that is confusing me the most:

* Desktop continues to work.
* The same Databricks host and HTTP path work there.
* But Power BI Online either fails authentication or throws this newer ADBC-related error when creating a new connection.

Has anyone successfully connected Power BI Service directly to an Azure Databricks cluster like this recently, without Premium capacity and without changing to a SQL warehouse?

Any guidance from someone who has dealt with Azure Databricks + Power BI Service recently would be hugely appreciated, because right now I am trying to determine whether the real problem is:

* stale OAuth credentials,
* Power BI Online’s newer Databricks connector behavior,
* a new service-side limitation,
* or a new network/gateway requirement.