How does randomness works in mnemonic phrase generation?

[Bitcoin]

How does randomness works in mnemonic phrase generation?

As far as I know, randomness in computers are not truly random, but rather pseudorandom, mostly derived from current timestamp. So when creating various wallets, I have saw a lot of them introduced some kind of user-generated randomness (like just moving the mouse) and then deriving the wallet and mnemonic phrase out of it, but some does not.

For example, TrustWallet or many others, you just install the app, it creates the wallet for you and you just write down the words.

Is not it possible, but highly unlikely, that two different people create the same address in the same time with the same wallet creator tool?

Or what if I set the timestamp to some certain precise number, would I be generating the same wallet like someone before me?

Source: How does randomness works in mnemonic phrase generation?