Macintosh HD Data shows my applications folder to be empty even though I've installed dozens of working apps?

Beginning with macOS 10.15 Catalina macOS now has a read-only APFS system volume called "Macintosh HD" while the "/Users" folder is on a read+write APFS volume called "Macintosh HD - Data". See this Apple article for more information:

https://support.apple.com/en-us/HT210650

FYI, there are also some other hidden APFS volumes now for normal macOS operations than are listed in the article.

You, my friend, are experiencing the dubious joy of using Apple's new APFS file system. Your brain may still be wrapped around the basics of the old HFS+ system, but things have changed.

Macintosh HD is a read-only protected APFS volume for macOS system files. There’s nothing you can do with it short of erasing the drive and all the data on it. That would be bad!

Macintosh HD - Data is the volume where the user accounts and user data live. Files and folders on this drive may be freely managed by the user accounts that own them.

Finder always displays both of these volumes together as a single drive named Macintosh HD. In Finder, the default volume that you are usually interacting with is Macintosh HD - Data. Finder never reveals the full name of the -data volume to you. But Disk Utility and Terminal will.

In Finder, when you click > Go menu > Applications (⇧⌘A), the window that opens is a representative of the folder located at Macintosh HD/Applications/. It's the default location for all the applications available to all the users of the Mac. This is where your applications are actually going.

The applications folder you see in your Home folder is located at Macintosh HD - Data/Users/yourusername/Applications. It lives on the -Data volume of your APFS installation.

It's a different animal than HFS+ format used in previous versions of macOS.

You can choose which items will appear in the Finder sidebar by clicking Finder > Preferences > Sidebar and then checking the appropriate boxes. These items will display in any Finder window once Finder > View > Show Sidebar is selected.

There's more to learn about APFS, but thinking about all of this makes my head explode. 🤯