To work with a computer you need a keyboard and a display.
Various variants are possible. The simplest is a mechanical keyboard and LED display.
The 6x4 matrix is a solution from the new (1990) version of the CA80. PCB for old calculator ELWRO 144. Some key descriptions need to be changed.
8 digit 7 segment multiplexed LED.
Documentation (klonca80.blogspot.com)