ok I got a #bitcoin bounty, I'll zap directly 10.000 sats to the first best answer to this question:

When you create a wallet of, lets say 12 word seed, and ad a passphrase to it, what happens really in the background?

I'm not a programmer, but I'd like to see the real thing in the workings when this happens, if you know what I mean. I know that you create a whole new wallet by adding the passphrase, but what happens with the code? what does the Bitcoin software do when one generates a seed + passphrase.

the answer can also be a good explanatory video or article.

Thanks for your time ! Btw you can verify my history that I always pay when promised