This seems to be a limitation on the current connector capabilities, which should hopefully be resolved in the future.
A workaround is to use REST calls/posts instead of the connector.
Medium blogs can be helpful for getting started, but they are not always fully accurate or up to date. For OData write operations in Mendix, it’s best to follow the official documentation rather than relying solely on blog posts.
I would recommend going through the steps again based on the Mendix docs here:
https://docs.mendix.com/refguide10/write-data/
This documentation explains how writing data to external OData services works in Mendix and clarifies that external entities do not behave like regular persisted entities (for example, there is no normal “commit”). If, after following the official guide, the entities still appear read-only, the most likely cause is that the OData service metadata does not expose the required CRUD capabilities.
Starting from the official documentation usually helps avoid confusion and aligns better with how Mendix actually handles OData write operations.