Shortcut to page up or page down one screen at a time in library module?

The Page Up and Page Down keys should work in Grid on both macOS and Windows. I use them all the time for scrolling Grid on my Mac. They might not work if Grid does not have keyboard focus.

Many compact keyboards (laptop and desktop) don’t have Page Up and Page Down keys. For those, on both macOS and Windows you should be able to combine the Fn key with the arrow keys, so for example you get Page Up/Page Down by combining the up arrow/down arrow keys with the Fn key. (Fn + left/right arrow get you Home/End, which also work in Grid.)

The Fn shortcuts for Page Up/Down, Home, and End don’t always work with some non-OEM keyboard brands. For example, the Fn+arrow shortcuts work on the keyboard built into my MacBook Pro, but not on the Logitech Bluetooth keyboard I sometimes use with the same computer when it’s in closed-lid desktop mode.

On Windows, the PgUp key and the PgDn key works. Is there a similar key on a Mac?

Try [Shift]+[fn]+[Down Arrow]