I seem to have tried everything suggested in answers to this same question. Today, June 13th, 2019, I accidentally moved some messages into the archive, and I know I've done the same thing in the past. I cannot find anything called "archive" or any messages that are not labeled as in my "inbox."
As mentioned, there is no "archive" folder in Gmail.
But I found a way to find only the messages sent to the "archive".
Write in the search bar:
has:nouserlabels -in:Sent -in:Chat -in:Draft -in:Inbox
In the search results you will see all the messages Which are not under any label (="archive").