Three bars means... the exact same thing the thousands and thousands of times it's been seen before.
People have no inate understanding of 'menu'. We don't even read short words like that letter by letter, it's read as a block and is far more complex than three bars.
People spend years specifically learning how to read starting in early childhood. It's expected in the current era that people above a certain age are literate to at least some degree. People usually don't spend years specifically learning how to interpret icons except when they have to in an app or on a sign they run into.
"Menu" has a consistent meaning (a list of items to choose from) which most people can be assumed to know. Icons aren't as easily parsed and take more of a mental load to reason about them. Or just trial and error to figure them out.
I've seen too many variants of icons for "general" menu. Three bars, three dots, square, square in square, tall rectangle, gear, company logo and probably a few more.
And if we want to focus on just three bars let's not leave out the skeuomorphism trend where three bars meant the "grip" area, something to use to rearrange items or windows.
> Three bars means what, exactly? There’s the cognitive load.
This was true early on when it was not a common convention, or only used in mobile apps. Now, it is nearly universal, though still not nearly standard enough in placement or presentation.
If we were to redo history, it would've been great to see an expanding menu closely positioned by a top-left logo. Sort of like a Windows Start Menu for each website.
Menu Settings Notepad
If these are actionable buttons, the message is encoded and decoded by viewers.
Three bars means what, exactly? There’s the cognitive load.