"There 100% is a cover system in BG3. It's called "putting a solid object between you and the enemy, so they don't have a line of sight to you." Enemies, at the very least, should know where the attack came from, and either attempt to investigate or take cover (which can include running away to get out of your weapon/spell range)."
Yep - last bit is a critical failure for current system. It makes 0 sense for an enemy to stand there and let you muder them, as you pop into and out of of 'stealth' continually. Unless they're mindless, like a zombie. As Mrfuji3 notes, they should seek cover and draw *you* out. Also, if you attack from stealth (or invisibilty), an enemy can make a guess as where its coming from and investigate. Or just lob some AoE effects into the likely area...This kind of lack of reactivity from enemies is completely immersion shattering - no DM would allow their party to get away with it (well, none I've ever played with)
