Ledger: is the private key tied to the device or wallet?

Context: I’ve had a Nano S since before, with one recovery phrase and a wallet with some small BTC on it. Buy a Nano X, set up with a new phrase, and a new wallet, and put some coins in that. Then I also imported the old wallet to the new device via Ledger Live, so there are two wallets. But then I started to wonder:

Is the recovery phrase by device or wallet, or how does it work? If someone gets my old phrase, can they also unlock my new device, or can they just unlock the old wallet?

It seems that it would be possible to unlock the old wallet with the new or the old expressions, but only with the new phrase the new wallet?

Been scouring through the docs but it doesn’t really tell how this works. I guess when I imported, it should have revived the same old wallet but with new keys? But he would want to be sure.

Not too worried about the old wallet, but the new. So if someone can still just restore the old one, I wouldn’t worry so much, but whether my new wallet on both expressions is somehow my question, or whether my new Nano X devices phrase is it is only?