Something similar occurs in both the Segmentations module and the Segment Editor module for the name of the Segmentation (and Segment?).
Maybe this is not typical of all users, but I had output an STL file with a rather long filename to try to keep track of the process used to generate it. (As I’ve said elsewhere, I may want to compare different attempted segmentations of the same anatomy.) I then reloaded it with the Data button as a segmentation, and with the existing name the panel at the left takes up a minimum of half my screen (note that the application is maximised in the above screenshot).
Interestingly, even if I switch to make a different Segmentation “active”, I still cannot shrink the pane.
Whereas for a file path it’s usual to put ellipsis at the start or in the middle (and then display the full path in a tooltip), for an object name I think it’s more usual to put the ellipsis at the end (and then display the full name in a tooltip).
—DIV