How do I restore accidentally deleted photos from my iPhone?

A couple of links might help: You can see this:

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

Basically the above says to look in Recently Deleted and in Hidden, as you've done. Be sure to check your Library thoroughly-- the pictures may not be where you expect, as dates may have changed. You can use the search field with the date or location. And remember, you can sort the Library by date captured or by date added. Also, your Library view now has filters, and you may not have your filter set to "All Items.”

Unfortunately, if you don't keep your own backups to an external drive, then there really isn't any place else to look. To back up your pictures you can just plug in an external drive, select the pictures, and use Share>Save to Files. Alternatively, you can backup to a computer:

Transfer photos and videos from your iPhone or iPad to your Mac or PC

If you haven't done one of those backups, then your remaining pictures continue to be in peril. 

If you have not been syncing your iPhone with iCloud Photos, your photos may have been included in your regular iCloud backups of the iPhone. In that case it would help to restore your iPhone from the last iCloud backup you made. But if you have been using iCloud Photos, the iCloud backup does not include the photos, and then restoring would be futile, also if it has been more than a day ago, that the photos have vanished. See: iCloud: Backup and restore overview

If you are lucky, the photos have not been deleted at all, but you may have only hidden them by hiding them or setting filters, see: Browse your photo library on iPhone - Apple Support

and Filter and sort the photo library

If your photos are not on device nor at iCloud.com, they do not exist. You can restore from the backups that you keep elsewhere of your important data.