With PhotoLab, it’s easy for the folder and file tree in the left panel of the PhotoLibrary to become too wide for the window:
The current solution (PhotoLab 4 on Windows) is to either drag the window separator to the right or to drag the scrollbar at the bottom.
I propose that PhotoLab also display the full filename as an overlay when the mouse pointer is positioned over the filename. This would be consistent with how Windows Explorer behaves and how a variety of other applications behave. This is how it looks in Windows Explorer: