It’s not only restart that requires that you re-hide the image browser in Customize, it’s every time you leave Customize and then return. This is different from how any other resize of the image browser works: resize it to any non-zero height and the setting is remembered, hide it completely and it isn’t.
Makes no sense, and it’s a real pain if you’re working on a smaller display and want to make better use of the space available.
For over a decade I have used Photo Mechanic to select the images to work with, in DxO or any other photo software. And it has worked perfectly fine ever since I purchased my first version of DxO OpticsPro, the predecessor of DxO PhotoLab. No, Photo Library is not necessary for selection purposes.