It's not your fault, but a bug which was recently found and fixed.
The fix is only in a beta version at present, but the beta has proven stable and should be fine to use. (As long as you don't mind some parts only being in English. The main delay in getting it into a stable release is in updating all the language translations.)
Please download and install Opus 12.2.5 (beta) (or a later version, for anyone coming to this thread in the future).
Then, go to Preferences / File Displays / Border and make sure Display as a toolbar is selected.
If there is a dropdown just under that for selecting which toolbar is used, you want to select the File Display toolbar. (This is the part which would not always be possible with Opus 12.2.)
If the dropdown isn't there at all, that's OK as it means the File Display toolbar is already selected.
Then click OK to close the Preferences dialog and things should return to normal.