The Finder Bottleneck
The macOS Finder (the default file manager) is highly visual. Instead of showing generic icons for your files, it utilizes a background process called QuickLook to automatically generate custom thumbnail previews for images, videos, PDFs, and documents. While this makes browsing local folders visually pleasing, it becomes a severe performance issue when browsing network-attached storage (NAS) or large external hard drives. If you open a folder containing thousands of high-resolution RAW photos or 4K video files, macOS will attempt to download enough of every single file to generate a thumbnail, grinding your network speed to a halt and causing the Finder window to freeze indefinitely.
Enabling Generic Icons
To speed up folder navigation and stop macOS from automatically generating thumbnails for massive files, you must disable icon previews in your Finder view options.
Open a new Finder window. Navigate to the specific folder that is causing performance issues (e.g., your network drive or an external photo archive). At the top of the screen, click on View in the menu bar, then select Show View Options (or press Cmd+J). A small floating configuration window will appear. Look for the checkbox labeled Show icon preview. Click this checkbox to uncheck it. The change is immediate. Finder will stop trying to generate custom thumbnails and will instantly revert to displaying lightning-fast, generic application icons (like a blue QuickTime logo for videos or a standard Preview icon for images). If you want this rule to apply to all folders using that specific view style (e.g., List view), click the Use as Defaults button at the bottom of the View Options window.