Thunderbird does not use the word spam or create spam folders. This would be from spam filters that your email providers uses. You might check with them.

Thunderbird uses the work junk and junk folders for this exact reason.

Hello,

what difference does this make? When I wrote "Spam folders" I actually meant the Junk folders that Thunderbird uses.

My question has nothing to do with my email provider.

My question thus remains unanswered: is it possible to empty Junk from the parent Junk folder (hereby deleting all Junk messages in the child folders of each of my mailboxes)? When I right-click the parent folder "Junk" I see not option for deleting Junk. First I must select a childfolder (so, the folder of a mailbox inside the Junk folder), and only then I can delete the Junk messages.

This means that every time I want to remove Spam (or "Junk" if you want) I have to delete this for every of my mailboxes separately. And since I have 10 mailboxes, this is not really comfortable.

I can imagine that it may be easy to add a function "Empty Junk" in the context menu of the parent "Junk" folder itself?...

The difference is where the filtering is done. If you say spam, like you did, it is not Thunderbird doing the filtering. If you say junk then it is a Thunderbird function. I answered the question as you asked it. You did not get the answer that you seemed to be looking for. That is the difference.