It took me a long time to figure that out as a kid. Listening to Beatles songs with lyrics like “the man in the Mac said you gotta go back” or “the banker never wears a Mac “ I had no idea what that was.

That's Mackintosh with a "k", isn't it? At least, wikipedia says (https://en.wikipedia.org/wiki/Mackintosh) this is the standard spelling of it. Although it also says its inventor was a Charles Macintosh (no "k").

McIntosh [1] is a type of Apple. At [1] you can also read about McIntosh ("McIntosh Laboratories") the hi-fi brand [2]. My father was an audiophile, and had various McIntosh hardware (pre-amplifier, tuner, oscilloscope, ...). Apple named the Mac after the Apple but deliberately misspelled it as "Macintosh" to avoid confusion with the hi-fi brand. As I grew up with the hardware from McIntosh (Laboratories), that'll for me always be real McIntosh. Even though the real one is the apple genus.

..and then there's "Big Mac". I'm not sure where that got its name from, nor if it has anything to do with McIntosh (labs or apple). It was innovated before the Mac was invented though.

[1] https://en.wikipedia.org/wiki/McIntosh_(apple)

[2] https://www.mcintoshlabs.com https://en.wikipedia.org/wiki/McIntosh_Laboratory