‘how to handle dynamic Linked Service connections in Azure Data Factory if the UI doesn’t naturally support the addition of parameters’. Depending on the Linked Service the support for this varies.
Well, the answer, or should I say, Microsoft’s quick hack answer, is use the ‘Specify dynamic contents in JSON format’ option available for all Linked Services regardless of there type/popularity. This feature enables an empty text box where you can define anything about the Linked Service. It also removes all other attributes from the Linked Service connection panel, except Title and Description.
What this setting does is basically allow you to write you own JSON definition (in full) for the intended Linked Service. This then gives you the flexibility to parameterise anything in the key/value pair structure and means you don’t need to worry about Data Factory naturally supporting the Linked Service being dynamic via the usual developer canvas and expression builder. The down side that I’ve already alluded to, is that if you only want one value in the Linked Service to be dynamic you’ll have to provide the complete JSON definition for everything.
— Read on mrpaulandrew.com/2020/07/14/how-to-use-specify-dynamic-contents-in-json-format-in-azure-data-factory-linked-services/