Hi,when you attack from darkness (and you see your target and your target does not see you) - do you get advantage on your attack?

I always thought so:

When a creature can’t see you, you have advantage on Attack rolls against it.
"If you are hidden—both unseen and unheard—when you make an Attack, you give away your location when the Attack hits or misses."

but I was told that because the target hears me attacking I will not have advantage on my attack (???) and I must Hide first to have advantage on my attack. Do I really need to Hide before attack to have advantage when I am already concealed in darkness (target does not see me)? I always thought that when target does not see me then it is enough to have advantage on my attack.Seriously, attacker vs effectively blind target has clear advantage in fight in RL imho. Being heard should just give away my location, so my target can attack back (with disadvantage), right?

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thnx for help