View ▸ Increase / Decrease Grid Thumbnail Size (view.thumbSizeUp / view.thumbSizeDown)
step the bottom-bar slider by 30 pt within its 90–480 range in Photo Grid, Square
Grid and People, as Lightroom Classic's Library Grid keys do; + also enlarges.
Detail, Compare, Survey and Reference ignore the keys, text fields keep them, and
⌘= / ⌘− still zoom the photo. The slider's range is now shared constants.