But if I understand correctly once the cursor’s “focus” is on one of the
adjustment panels, the Tab and Shift-tab work only within that panel.
To return the focus to the Filmstrip panel, you need to click on that panel.
If one of the adjustments is active try Ctrl+Right or Left Arrow key
Camera Raw Keyboard Shortcuts for Windows (filmstrip mode)
Move Up One Image
Up Arrow or Ctrl-Left Arrow
Move Down One Image
Down Arrow or Ctrl-Right Arrow
Or you can press Enter and then use the Up or Down Arrow keys