How to use mockups correctly?

Question

Layouts and prototypes

I have repeatedly seen website templates that use iPhones and iPads as mockups. Download similar mockups. Double-clicked, as expected on the smart layer. A 2000-3000px wide window opens. But after all, the design for the mobile version is made approximately 300px wide. Question: how to shove the mobile version into a mockup of such a large width? I phrased my question as best as I could, I hope it's clear :)

Answer 1

In general, good mockups are usually well documented.
Where does the 300px figure come from? Maybe 300pt? In any case, in the modern world, web design should be based on density-independent pixel, since we have both 720p tablets and smartphones and 720p and QHD. And the layout built according to dip's is no longer a problem to display in the desired resolution

Answer 2

But after all, the design for the mobile version is made approximately 300px wide.

Rukalitso, "tentatively"... are you a web designer after all this?