While using Windows terminal (Preview) for quite some time, I always opened up the Terminal and then opened a second Tab with my WLS instance. Doing this multiple times a day, this ends up in many many unnecessary clicks.

To change the default behaviour open the Settings (can be found at the right drop-down arrow of the Terminal tabs).

This will open up the settings JSON file. Look up for the defaultProfile entry and search for the corresponding GUID (the string behind this setting) in your document.

Change the GUID in the defaultProfile to the one identifying your prefered terminal.

Save it, close the file and save a lot of clicks.