Photos from different cameras and different phones arrive at different sizes. Making them match is a single batch operation.
Crop each photo to a common ratio before forcing identical dimensions. Locked resizing preserves each source's shape, so heights may differ; forcing dimensions without first cropping can distort mixed-shape originals.
Locked resizing keeps each image's proportions. Fixed dimensions can stretch images; crop to the required ratio first.
The encoder creates a new file. Upscaling cannot recover detail that the original did not contain.
Giving every photo the same width does not give them the same shape. A portrait photo and a landscape photo at the same width come out with different heights. If they need to match exactly, crop them all to the same shape first with Crop & rotate, and then resize them to the same width.
The other way is to switch off Keep the original shape and force an exact width and height. That makes every picture the same size, but it stretches any that are a different shape, so it only suits photos that are already close.
No. Check dimensions here, then use Compress to a size if the destination separately limits file size.
JPG, PNG and WebP always open. A phone may run out of memory with a big batch of large photos, so add fewer pictures at a time or use a computer.
With the shape lock on, the width is applied and the portrait one comes out taller. Crop them to the same shape first if they need to match.