When adding images using the page builder templates you can choose to crop the images to the same ratio as the templates, zoom in and out or select no-crop to ensure your images maintain their aspect ration.
Cropping images to match template
When using the page builder you can drag across an image from the templates on the right hand side panel.
When you hover over the image click the camera icon to replace the image.
By default, your new image will be cropped to the same dimensions as the original template image.
This can sometimes result in pixelation of the image if the image you try to upload is too high resolution. You can either optimize the image before you upload it using a tool like https://imagecompressor.com/.
If you want to maintain the dimensions of your own image and not crop it to the size of the template you can click the three dots in the image toolbar, then check "No crop" and then click "OK"
This will result in your image maintaining its own aspect ration and will not crop it at all.
You can zoom in and out of the image using the + and - icons. Again you should optimize the image first if you wish to zoom and image.