Comment by kccqzy

Yeah I'm pretty sure that setting has been there since Yosemite. That was the version that first prominently featured blurred translucency. (The transparency in earlier versions like Mavericks was really subtle and would not need such a setting: see for yourself in this image found by Googling https://i0.wp.com/morrick.me/wp-content/uploads/2021/02/001-....)