Your first picture shows the folder in the ...default-release-2 profile. Open Help/More Troubleshooting, about:profiles. Is the active profile ...default-release-2 or another one? If it's another one, copy the mbox files such as Curtze (ignore the Curtze.msf file) to Mail/Local Folders of the active profile, with TB closed.

@sfhowes, thanks for your feedback. I attached the screencap for the default profile. At the same time, I created a new folder within the inbox "curtze_new" and now it's showing on TB nav pane and the local folder thru windows explorer...hence I kinda guess I'm on the right directory.

So with the new one, "curtze_new" is showing but not "curtze". This is just one example but there are other folders that are not showing...but they're visible through windows explorer (under the same directory)

Try deleting Curtze.msf, with TB closed, then restart TB, which will automatically rebuild the msf file. Does the Curtze folder then appear under Local Folders?

closed TB, deleted curtze.msf, launched TB, curtze folder still not appearing...and confirmed thru explorer curtze.msf is no longer there (not sure when .msf will be rebuilt)

Rebuilding the index file shouldn't take very long with a 100MB mbox file, so if it isn't, it suggests to me the mbox is corrupted beyond repair. I would try to convert it to eml files using one of the many tools, such as this one. If the eml files look OK when opened in TB, they can be imported to Local Folders by drag and drop from File Explorer to TB.

I finally figured it out. For some odd reason, via Explorer, the invisible folders are marked as "hidden" (when you use right click on the file..in this case "curtze"). I shutdown TB, via Explorer, select the ones that are invisible, right click, properties, and uncheck hidden...and Voila...now it's showing.

Thanks for the help!