Crop first, then scale
The selection always has the 16:9 shape of the output, so nothing gets stretched. Drag it to move, scroll to zoom and use the handles to resize. The label under the frame shows how many source pixels you have selected.
Aim for “1:1 ✓”
When the selection is exactly 1920 × 1080 source pixels, the file is a straight copy: sharp text and the smallest file. Crop 1:1 sets that for you on screenshots larger than Full HD. If the badge says downscale, text gets softer; if it says upscale, the screenshot is smaller than the output and the result will be blurry.
Screenshots from HiDPI screens
On a Retina display or Windows at 200%, a full-screen screenshot is twice as large as it looks, e.g. 3840 × 2160. Scaling it to 1920 × 1080 halves it exactly, which keeps text clean. For a smaller part of the screen, Crop 1:1 usually gives the sharper result.