What is safest way to store users wallet private keys for a sniper bot? Encrypted keys I have already stored but after seeing recent incidents with unibot and maestro need to know if there is much more secure methods available

you cannot make it safer.
They're stored on a server not owned by you, end of story :P
apply a risk management to those keys
eg: never store more then 1000$ on it, if goes up, transfer out account.balance - 1000 to safe wallets.
Add or remove zeros based on your allocation

I preferred storing crypto in contract and only allowing users to make txs based on their allocated amount but still it's not 100% secure. I found privy.io(used in friend.tech) did it with login tokens to secure but they are also unsafe

Because here users wil think they don't own the crypto. Do we have any third party provider or library which allow uses like we have on dydx