Open the photo in the Photos app
Click Edit
Click Crop
Drag the corners or edges to adjust the crop
Use the aspect ratio options if needed
Click Done
Open the photo in Preview
Click the Markup toolbar button if needed
Select the rectangular selection tool
Drag to select the area you want to keep
Click Tools
Click Crop
Open the image in Quick Look
Press Spacebar to preview the file
Click the Markup icon if available
Use the crop tool if shown
Save the changes
Open the image in another app like Pages, Keynote, or third-party editors
Use the crop tool in that app
Save the edited image