Cannot Find a Mailbox on Apple Mail

I have a folder somewhere in Mail that I cannot find. When I do a search for the name of the mailbox, all the items that I've put into it over the years appear, as they should. Selection of any one of them shows the mb in which it is stored, and it is the one I'm seeking to find, i.e., this is how I know it still exists.

When I go through all my nested mbs in my Mail, it is nowhere to be found. I found a solution here from 2015 that I tried, by using the "GoTo" folder and providing the code given, removed the content and restarted my Mail. It took about a half hour, but finally finished. Everything in tact, but I'm still stuck without my target mb. Suggestions anyone?