First off, I notice you are on iOS 26. Because beta software is still being tested, there are lots of issues present and this can be attributed to your data loss. The only thing we could hope for now is that you had an iCloud Backup that wasn’t overridden, or an archive on your computer to restore from that hopefully has all your photos. The first thing is to restore back to iOS 18.5. If you have no backup or it was overridden, your photos would likely be gone.
How to uninstall iOS or iPadOS beta software - Apple Support
If you restore and the photos still aren’t there, when was the last time you backed up your iPhone? The iCloud Terms and Conditions state that if you haven’t backed up your device within 180 days, they reserve the right to delete any existing backups, which can include photos and videos.
Legal - iCloud - Apple