How to retrieve lost data?

If you are using iCloud Photos to sync your photos, having them still stored in the "Recently Deleted" album is the only way you can restore them:

If you're missing photos or videos in the Photos app - Apple Support

Delete and recover photos and videos on iCloud.com - Apple Support

An iCloud backup does not contain photos if you are syncing your photos to iCloud.

ensure you have daily automatic backups on your iCloud and that there is enough iCloud storage. if you are attempting to restore via backups that you have on your iCloud but photos and videos are still missing then sign in to your Apple account and chat/call Apple support. There will be able to recover most or all recently deleted photos and videos EVEN IF you have deleted them from your recently deleted folder.

It worked for me and was able to recover 4500 photos and 400 videos