To follow this blog, you would need an SAP Business Technology Platform account. I got a Pay-As-You-Go account that lets me get started for free. Then cost based on usage:

The trial version of the BTP does currently not provide access to SAP Data Sphere.

I then follow How to create an SAP Datasphere service instance in the SAP BTP Platform? By Jeetendra Kapase.

To access SAP Open connectors Subscribing to Integration Suite is required.

Subsequently I add Extend Non-SAP Connectivity via Manage Capabilities -> Activate Capabilities:

As a result, I got access to Open Connectors:

There I find my Organization and User Secret that I need to Data Sphere to Open Connectors:

To do so, I go into Connection where it is possible to Integrate you SAP Open Connectors account:

Where I chose my SAP BTP Account Region and provide my Open Connectors Organization and User Secret:

This gives me access to my Open Connectors from SAP Datasphere:

Which allows me to connect to several third party data sources powered by SAP Open Connectors, e.g. GitHub for which I created an instance:

I then Chose Connection Type Open Connectors which presents me with my Open Connection Instance:

And get my Datasphere GitHub connection:

Therefore, if you cannot find the Connector Type you need from the standard SAP Connector Type offering, I would recommend to connect to your SAP Open Connect Account.