The only thing I know of is to edit a title clip and increase/decrease the zoom but this won't change dimensions itself (editing dimensions like height increases width too)

Gwenview allows you to resize images. The option shows up in the left hand menu on my system when you open an image. Gthumb (need to install) is even better for this as you can resize multiple images at the same time. It would be good if Gwenview allowed you to do multiple files. Cheers.

No option appears for me (I am editing it via title clip) 18.08.2

oxo wrote:The only thing I know of is to edit a title clip and increase/decrease the zoom but this won't change dimensions itself (editing dimensions like height increases width too)

Transform effect allows to adjust width and height independently. Just check Distort and click the chain link icon between the two fields, then enter the values you want or click on the W or H and then drag the mouse to the left or right to increase or decrease the values. You can also grab the corners of the red transform shape in the project/clip monitor to adjust the size and ratio.

oxo wrote:No option appears for me (I am editing it via title clip) 18.08.2

I recommend you switching to 20.12.1 (use the appimage if necessary).