There are magic items that can be attuned to as helmets, but the helmets stopping crits is a thing from BG1+2 I think (I might be remembering wrong). It is homebrew but I don't mind it too much cause there is precedent, however if it turns out to be too unbalanced I wouldn't be sad to see it gone
This is correct. Helmets in Bg1 and 2 prevented critical hits, but for some reason did not help enemies wearing them.
As in Bg1 and Bg2 many hardcore AD&D players complained about this homebrew change and many others that Bioware made in regards to these games.
Its almost...like...history is...repeating itself.