Photos and videos disappear from the gallery
I'm losing some videos and photos from my iPhone's gallery from 2018 to the present. What is the reason? Is it possible to recover the photos and videos? I haven't deleted these photos or videos.
You don't say what model you're using, or what iOS it's running, which makes it harder to discuss what's happening.
Were these photos and videos taken with your phone, or were they imported from some place else, like a computer? If they were imported, some transfer techniques other than iCloud Photos are intended to be temporary.
If you don't use iCloud Photos, but you have Settings>Apple ID>iCloud Backup turned on, then you may be able to recover data from the last 30 days or so. You should look here:
Restore your iPhone, iPad, or iPod touch from a backup - Apple Support
“Restore” is what you do when you buy a new phone, so this safety, if you have it set, requires you to erase everything on your phone and replace it with the backup.
If you don't keep your own backups to an external drive, then there really isn't any place else to look.