How do I open a DTSX file in Visual Studio 2019?

The error message indicates you are trying to open a project/solution. DTSX is a package.

You first need to open the .sln or .proj file. Within the project (solution explorer) you can open the dtsx. Do not try to open the dtsx file from the source control explorer as that does not open with the project references.

In summary, open the solution/project, then open the package from the solution explorer.

You will have to install SSMS, SSAS from VS Extensions> (In VS Menu, click "Extensions" and then "Manage Extensions

To edit and create integration services packages (.dtsx) is necessary to install SQL Server Integration Services Projects. After installation Visual Studio 2019 can create or edit integration packages either independently (open file) or in Integration Services Project. It is also possible to open packages on SQL server even when SSMS fails with message:

Connecting to the Integration Services service on the computer "xxxx" failed with the following error: "Access is denied."