The short answer
Hidden photos transfer with the rest of your library and stay in the Hidden album on the new phone. If you use iCloud Photos, they are already there when you sign in. If you restore from a backup or use Quick Start, they come across with the library. Nothing about hiding a photo keeps it on the old phone.
How each transfer handles hidden photos
- iCloud Photos. The library syncs to the new phone, Hidden album included. Nothing to do.
- iCloud backup or computer backup. The library is part of the backup. Hidden photos restore hidden.
- Quick Start. Moves the library directly, hidden state included.
- Selective transfer. If you only move some photos, the Hidden album is easy to forget. Check it before erasing the old phone.
If you did not want them to come across
Delete them from Photos and from Recently Deleted on the old phone before the transfer, or before the new phone signs in to iCloud Photos. Once they are in iCloud Photos they are on every device on the Apple Account.
Vault photos are different
Photos in Kryptis are not in the Photos library and do not move with it. To move a vault, make an encrypted backup on the old phone, restore it on the new one, confirm it opens, then erase the old phone. Step by step.
That difference is the point. A hidden photo goes wherever the library goes. A vault photo goes only where you put it.
