The Location column is always empty, for any type of account, for any folder, when it's selected in the Folder Pane. Location is only useful when viewing global or classic search results that combine messages from multiple folders. I see that this might be relevant when viewing the All Mail folder, but many users unsubscribe to All Mail (see All Mail section).

As an example, press Ctrl+Shift+F, then select the gmail account at the top, and enter a search filter, then display the Location column in the search results.

Thank you, that is helpful. Not sure why it is available for display in the folder view ... :-(

So far I am "afraid" to unsubscribe to "All Mail", as I don't always seem to find some of my wanted mail anywhere else! Gmail labels & sorting just don't match my own expectations & logic.

I download to Thunderbird (which I have used for many years) via IMAP, and struggle to understand & tolerate Gmail. Deleted & moved emails seem to reappear, lingering in various label/folders unexpectedly, etc. Confess to frequent frustration, even misery!

I had hoped the location column would be useful in All Mail to find and/or remove emails, but I guess not!

Here is a way to view a kind of 'All Mail', or any collection of folders, with the Location column not empty: File/New/Saved Search..., enter a name and location, and click Choose... to add all the folders except All Mail, click Match all messages, Create. The Location column in the saved search shows the folder name for each message. You can of course create other saved searches with different folders or filter rules to search according to age, senders etc.