Was that the full screen? There should be that titlebar that Jackie mentioned.
Double clicking docks it. But you might like the Floated version like I do.
It seems it some how got convinced to Be a full screen (height), which anchors in the corner
If you can't get to the titlebar (now missing a Top monitor)
set the focus to the TOC pane . Use Alt-<space> Move , then the arrow keys to move the titlebar into view
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