The crop tool doesn’t work properly in Photopea, at least in Chrome on Windows 11. To get around that, just choose the Crop tool, drag the handles to get your desired image size, then triple-click anywhere on the image. You’ll get the crop you want.

To get rid of the subsequent dimness of the image – and get back to regular editing mode – just click again once, anywhere on the image. Voila!

Did that work for you? Please share your insights via a comment. Thanks!