I'm working on a project that creates a new wallet for the user that is not controlled by them, what would be the safest option for storing newly created private keys programmatically?
A wallet that its user does not control it, don't fool me, but maybe you did not express your idea correctly as you wanted.
It's your private key, it's your bitcoin and it's not your private key, it's not your bitcoin. Your wanted wallet is like custodial wallet, that does not give its user private key, and don't give any bitcoin to their user technically.
I don't want to make you sad, but it is not a good and safe wallet for Bitcoin users.
https://www.youtube.com/watch?v=AcrEEnDLm58https://www.lopp.net/bitcoin-information/recommended-wallets.htmlWallet Basics:
Do not use wallets that don't give you recovery data; these wallets are likely controlling your keys.
Do not use paper wallets unless you're an advanced user who understands all the risks.
Do not store large amounts of value in single signature wallets.
Make sure your heirs know how to recover your wallets without you!
Your wallet is likely controlling keys and users are not controlling keys.