It seems Umbraco Forms API doens't have an endpoint to fetch record data, e.g. to show data after submission. https://github.com/umbraco/Umbraco.Forms.Issues/issues/1225 Has anyone had a similar issue and eventually created own API endpoint to handle this?

We haven't but I'd make a simple Umbraco API controller that uses

IRecordStorage

and its friends to "supplement" the Forms client-side API and the Content Delivery API. I'm guessing there's a way to actually extend the Content Delivery API to provide this, though.