where is the menu button on a desktop mac computer

¿do you mean this?

Menu-key:

The key's primary function is to launch a context menu with the keyboard rather than with the usual right-mouse button. It can be used when the right-mouse button is not present on a mouse.

from:

https://en.wikipedia.org/wiki/Menu_key

If that is what you seek, the Control key (either side of the keyboard on keyboards so equipped) can be held down while you click the primary mouse to obtain a secondary-click or right-click to show the contextual menu.

Most of the initial features and functions of the main macOS (OS X) are within specific applications

and the other settings allow access into system, via desktop or main Finder menu below Apple icon...

{The Finder allows access to many control elements in lists beneath each column in this main menu.}

As mentioned in previous replies, there is no "menu button" in the Apple Macintosh. Several icons

in the Dock can allow access to other content that may not be duplicated in the 'Apple Finder' lists.

And 'system preferences' allows settings to be changed in various segments of the macOS/X.

Mac Basics: Desktop - Apple Support

Elements of the desktop. Apple menu ... If using Mac OS X v10.6 or later ...

https://support.apple.com/en-us/HT201956

10 Mac OS X Tips For Finder, Menu Bar, Context Menu & Navigation

10 Mac OS X Beginner Tips For Finder, Menu Bar, Context Menu & Navigation... you will

find two radio buttons, ... Mac OS X How To Hide Menu Bar Icons On macOS. Web...

https://www.addictivetips.com/mac-os/10-mac-os-x-t

Chapter 3. Voice-Over: Learning Mac OS X Basics. ... You'll learn how to use menus,

buttons. Use the Action pop-up menu to choose commands for the item selected in the

https://www.apple.com/voiceover/info/guide/_1122.html

You may need to re-phrase your question to ask for specific control elements you need to access.

Good luck & happy computing! 🙂

The term "Menu Button" does not appear to be widely used. When searching, your post is the first one that comes up, and the rest are largely unrelated.

what are you trying to accomplish?

What menu? What Mac? What operating system?