When you are specifying the target for your creative in intercept; select My Custom URL instead of survey selection dropdown. Enter preview link of your survey and test it out.

Hi,
We just started another testing and I worked with the suggestion of using the "custom url" with the preview link.
However, in the creatives, the preview link automatically jumps to the Mobile preview, with the smartphone-borders!
Is there any way to avoid that? Some url parameter perhaps that disables the mobile preview?

Hey,
IF the survey is opening in the new tab, check the dimensions of the new window if they are small the preview will automatically jump to mobile version.
Maximize the window or turn off the mobile view toggle.

No, the surveys are not opening in a new tab. They are opening in Feedback button sliders or in popups.
We then settled down on instructing our testers to indeed just turn off the mobile view within the smaller popup windows (we didn't find a way to automatically, default, turn that mode off),
but on some browsers the menu to do this, doesn't properly show.
Here's an example of a button-slider and a popup on a browser in which we get the corrupted header menu (above), and an example of the button-slider as it should appear with the proper menu (below).

I opened a ticket for Qualtrics Support, and their reply was:

Unfortunately, the preview link isn’t supposed to be used as a target for the intercept. You would need an actual survey for testing.

Your only other option would be to use copies of both the survey and the intercepts, and use bookmarklets to test them on the needed websites.

We apologize for this inconvenience!