What types of keyboard layouts exist? Among #1, which keyboard layouts are optimized for disabilities? Are any of #2 better for those with limited fine motor control?
Keyboard layout
Fine motor control involves making small, precise movements like painting or typing.  The standard keyboard layout is designed to be used by someone without any motor control issues. There are modified keyboards for multiple types of disability.
any specific mechanical, visual, or functional arrangement of the keys of a keyboard or typewriter
Could someone with fine motor control issues benefit from an altered keyboard layout?