photos from certain days are black

You may try some of these steps, please check after each step...

1. Sometimes, a simple restart can resolve temporary software glitches. Turn off your iPhone, wait for a few seconds, and then turn it back on.
   1. Restart the device. That's it.
   2. Still not solved --> Force restart iPhone - Apple Support
2. If the issue persists, you can try resetting all settings on your iPhone. This will not erase your data but will reset all personalized settings to their default values. Go to Settings > General > Transfer & Reset > Reset > Reset All Settings and confirm the action. Note that you will need to reconfigure your settings afterward. All settings—including network settings, the keyboard dictionary, the Home screen layout, location settings, privacy settings, and Apple Pay cards—are removed or reset to their defaults. No data or media are deleted.
   1. Reset All Settings: Return iPhone settings to their defaults - Apple Support:- Return iPhone settings to their defaults
   2. You can return settings to their defaults without erasing your content.
   3. If you want to save your settings, back up your iPhone before returning them to their defaults. For example, if you’re trying to solve a problem but returning settings to their defaults doesn’t help, you might want to restore your previous settings from a backup.
3. Make sure you have the latest updates installed.
   1. Update Over-the-Air (OTA) —> Update your iPhone or iPad - Apple Support (IN)
   2. Update using iTunes/Finder —> Update your iPhone, iPad, or iPod touch - Apple Support (IN)

If none of the above steps resolve the issue, it is recommended to reach out to Apple Support or visit an authorized service center for further assistance. They can provide specific guidance based on your device model and iOS version.

Please check the following

1. When you create a backup of your iPhone using iTunes or iCloud, it captures a snapshot of your device's data at that specific moment. If you later delete any data from your iPhone, such as photos, messages, contacts, or any other information, and then perform a new backup, the deleted data will also be removed from the new backup. The backup process essentially reflects the current state of your iPhone, and any changes made to the data will be mirrored in subsequent backups. So, be cautious when deleting data from your iPhone, as it will be permanently removed from future backups as well. If you wish to preserve specific data, it's important to keep it on your device until after the backup has been completed. Backup methods for iPhone, iPad and iPod touch
2. If you sign out of Apple ID sign backing with another Apple ID after you had turned on Messages in iCloud & iCloud Photos, your content is safely stored in iCloud and is available on all devices that use the same Apple ID.
3. If you have restored your iPhone with a backup that does not contain the Photos that you are looking for then please look for the correct backup on your PC/Mac --> Locate backups of your iPhone, iPad, and iPod touch - Apple ...
4. Do you have a correct backup (iTunes) --> Restore your iPhone, iPad, or iPod touch from a backup ...
5. If you have restored from iCloud backup, then note the following
   1. iCloud backup doesn’t include information that is synced and stored in iCloud, like Contacts, Calendars, Bookmarks, Mail, Notes, Voice Memos, shared photos, iCloud Photos*, Health data, call history, and files you store in iCloud Drive.
   2. *-If you had turned on iCloud Photos, your content is automatically stored in iCloud and is not backed up.
6. Probably you may have un-synced photos with Mac / PC, sync them again
   1. For PC: --> Sync photos in iTunes on PC with devices - Apple Support
   2. For Mac --> Sync photos between your Mac and iPhone or iPad - Apple ...
7. Have you ever imported your photos to Mac/PC and used "Delete After Import" --? Transfer photos and videos from your iPhone, iPad, or iPod ...
8. If not found anywhere, have you ever uploaded them to any Cloud Drives (iCloud Drive, Google Drive, OneDrive, DropBox, Flickr, box, AmazonDrive, Adobe Creative Cloud etc)