backup old photos in icloud

Alright, first of all, I had an iPhone 8 Plus, okay, and it was on iCloud. Later on, I got another one, and that iCloud had 18,000 photos. Then, I subscribed to this family plan for iCloud with someone else. After that, I did get the second phone, which was an iPhone 14—and I used the same iCloud account on both phones.

At that point, I signed out of that family plan, and there wasn't enough storage, so I backed up all the photos. Suddenly, 10,000 photos disappeared, and when I tried to recover them, after a couple of days, all the photos on the phone were gone.

By mistake, I synced the photos between both phones and the iCloud, so the photos that were on the new phone ended up on the old phone, and the old phone's photos got lost. So, trying to recover them didn't work. I formatted the old phone, restored from the old iCloud backup, but it said that the phone wasn't up to date, so it wouldn't restore properly. I tried the second phone, the iPhone 14, and it still didn't restore the older photos from that backup.

So now, what should I do to get back those old photos?