iCloud
last night I deleted a bunch of photos and I deleted one by mistake.. I went on iCloud to see if the photo was still there but it’s not.. before iCloud used to save all my photos even if I deleted them on my iPhone
iPhone 11, iOS 14
It should be in Recently Deleted (both on your phone and on iCloud) and you should be able to recover it on your phone. See: If you're missing photos or videos in the Photos app - Apple Support