Help menu > Troubleshooting information. Scroll if necessary to "profile folder" (it is the 11th item in the table) Click the button that says open Folder beside it.

That is all.

I tried that, and when I selected the "open folder", it says the location is not available. I followed the path where it says the profile is supposed to be, but when I got to ".../AppData/Roaming", there was no "Thunderbird" directory. I'm displaying hidden items.

You might try going to Windows File Explorer and click View>show>Hidden Items

Is there anything odd about this machine from a home computing perspective, like is it connected to a network. Or are you using Thunderbird portable? It does not leave a file in the roaming folder, just some magic it's wrapper does, everything is stored with the application on the potable drive.

another thought. Was Thunderbird set up using another user account? Like perhaps the admin account?

I have a laptop (windows 11) and a desktop (windows 10) on home wifi network. The user name for each is different. Intent was to have both computers run Thunderbird and both receive the gmail. I downloaded Thunderbird to new computer and thought I set it up. Note that when I check "About Thunderbird", it says it is Thunderbird Windows MSIX package. It was not set up as admin. In hindsight, I'd like to get the profile from old computer (local folders, etc) on to new computer.

So you downloaded from the Windows app store, is that correct?

That is correct

I think the profile for the store version is in C:\Users\username\AppData\Local\Packages

Where the Profile for Windows Store version of Firefox can be depending on if you already had Profile(s) with normal version.

https://www.reddit.com/r/firefox/comments/qydvym/psa_windows_store_ver_preventing_accidental/

I wonder if this is the same with Thunderbird.

Thanks for everyone's help. However, still haven't found the profile. I have decided to uninstall the installation from the Store, and download it from Mozilla. Then, I'll be able to copy the profile from my desktop to the new laptop.

I have found the problem, I just have no idea what the solution is.

I think reinstall from the thunderbird.net site where the installed application will store things as advertised. Apparently the store apps are installed to run in some sort of virtual environment and profiles are stored in appdata\local in keeping with the use of MSIX packages. Mzla announced they had a package on the store, but no one said anything about either the complete failure of Mozilla to fix bugs in the troubleshooting information for years now that it reports an incorrect location for the profile, or that these special installed also has a special location for the data including the profile. I had to get that information from Microsoft.

My issue based on about Zero real information so far. I have no idea how resilient this appdata\location store is to hold mission critical information that is not stored in the cloud. The Firefox experience is no indicator as they have sync to fill gaps. At this point, Thunderbird has nothing.

Thanks Matt. I appreciate the time you (and everyone else) spent looking into this. Nice summary of why I was having the issue. I will be uninstalling and downloading from the thunderbird site.