I want the pictures of the posts which are displayed in a query loop to have the same size on desktop. Please have a look: https://prnt.sc/nKQUri2AbSeo
select the Image block inside the Query Loop, in it settings you can first set an image size.
Then set its width and height and set the Object Fit to Cover. Note that this may crop larger images/
For best practice, if you can crop and size your images to the same aspect ratio before uploading then it will be much better 🙂