In inventory, with the guidebook open, at a GUI Scale of 5 or higher in full screen, I cannot select the top right three inventory spaces. If guidebook is turned off I can access all of the inventory. Setting the GUI Scale to 4 or lower this is not a problem. Attached screenshot the mouse pointer is in the center of the top right inventory slot.
My workaround is to push F11 twice, then I am able to access all of the inventory items with the guidebook open.
See MC-143776.