You want to find the largest photo among all your Photos? The file size is shown in the details section below the photo when you view a photo enlarged and open the Info for it. But we cannot search systematically for the items larger than a given limit.
You may want to filter by the media kind:
- Videos tend to need more storage than image files.
- Live Photos are larger than still photos because of the added video component with the animation
- Portrait Mode photos are large because of the additional depth map.
- RAW photos are much larger than JPEGs, and JPEGs are roughly twice as large as HEIC files of the same quality.
i would first check the potentially large media kinds, if there are duplicates or boring items that you could get rid off.
Are you using iCloud Photos, Dove? If yes, do you already have "Optimize iPhoto Storage" enabled? The optimize option will automatically reduce the size of Live Photos or Portrait mode photos and keep the additional depth map or video component inly in iCloud, if yu need more free storage, also remove photos you have not used in long time and keep them only in iCloud.