On a macbook (unibody late 2008) the trackpad is unresponsive after normal boot. The arrow simply stays in the upper left corner. Adding a cable Apple mouse does not solve the problem. Neither do safe mode, resetting of PRAM, or other of these fixes: (see https://www.technobezz.com/macbook-trackpad-not-working-fix/)
However, after booting from a USB-stick, the trackpad works fine! So I think it must be a software issue. I have inspected the plists in the Library folder at the root of the normal startdisk, but found no plists appearing to be related to the trackpad or mouse. However, in the individual users library such plists occur, but are these really loaded before logging in?