In SQLServer Integration Services, the use of Expressions to replace properties at runtime is very powerful. You can use it in combination with variables to pass parameters to queries, determine runtime specific dates, and much more.
However, while testing SQLServer 2019, I came across the following issue when replacing the ConnectionString property of a Connection Manager using Expressions. This was addressed working with Microsoft and a fix will be released in a future SQLServer 2019 CU for this specific problem.
Read more : https://www.mattiasdesmet.be/2020/05/12/error-replacing-connectionstring-property-using-expressions-in-ssis/