A party member was blinded in a fight I shall not name (no need to spoil).
He could not do any attacks at all : neither using a dagger on an adjacent target (who was sleeping), whether manually clicking the attack button or clicking directly on the target. I could also not use a ranged cantrip. For those who do not know the mechanics : the description in-game of the Blind condition and the 5e rules both state you have Disadvantage on attacks (and you also, in 5e rules, lose the capacity to do Attacks of opportunity). But in this case, he could do nothing at all (luckily my cleric did the spell Restoration).
Steam profile : https://steamcommunity.com/id/baraz/
Is this the Blindness spell we're talking about? As I just blinded a necromancer and he simply had disadvantage on his Chill Touch attacks. Of course it might be just a bug with PCs, not NPCs.
Yep, a creature did the Blind spell on my Wizard, who failed his Con Save.
As you say, it probably works fine on NPC/AI who target using programming logic.
I guess you can cast Blind on a party member and test it.
Steam profile : https://steamcommunity.com/id/baraz/