Would you please post a screenshot that shows the sent folders in the folder pane?

I'd like to but screenshot won't post to this screen (Ctrl+V)

Use the "Browse..." button.

Hope this helps

Thanks. According to their icons, both folders are server (privileged) folders, that is, neither was created by you. Since you use gmail, this may help:

https://support.mozilla.org/en-US/questions/1510895

By the way, a common recommendation on this forum is to unsubscribe from All Mail because it creates copies of all gmail messages, doubling storage requirement, slowing search, et cet.

Many thanks. All resolved.