To set up the new Windows MIDI Service, you need to install a Setup tool, which, as of this writing, is only available as an unsigned beta app.

With the latest version of the Setup tool (2.38), you can create "MIDI 1.0" ports, which is necessary if you want to replace loopMIDI ports without reconfiguring the plugin ports.

The tool is, as mentioned, an unsigned beta app, and to install it, you must temporarily enable "developer mode" in Windows.

Go to Settings - Advanced - Developer Mode and turn it "On". You will see a confirmation popup where you need to click "Yes". The only purpose of this is to allow the installation of the unsigned beta app; you can disable developer mode afterward if you want.

To download the setup tool you need to browse to the following page:

https://github.com/microsoft/MIDI/releases

Under the heading "App SDK and Tools Release Candidate 3," scroll down slightly to find "Assets," and click on the text to open the assets section. Then, click on the marked links to download the tool for X64.

Once downloaded, run first the loopback file, then the SDK file. You will see a pop-up window that says "Windows protected your PC." You get this window because the app is not signed. Click on the "More info" link to get the "Run anyway" button. Click on "Run anyway" to finish installing the tool.

Click the Windows start button, search for "MIDI," and open the app.

Click the icon with "1.0" attached, then "Create New Basic Loopback Endpoint".

Enter "StreamDeck2Daw" (or whatever port name you want to create) in the "Loopback Name" field, and click OK.

Repeat the process to create the port for the opposite direction (e.g., "Daw2StreamDeck").

Create additional ports the same way, if needed.

Done, you can uninstall loopMIDI, and switch off developer mode if you want.

If you see an "Unable to create loopback endpoint" error popup when creating an endpoint, try restarting the MIDI Service.
Once the MIDI Service is restarted, try creating the port again.