https://www.pixilart.com/draw#

http://wiringpi.com/news/ use wiring pi to create a shimmed version of the main keypad library https://github.com/Chris--A/Keypad

https://github.com/oldbridge/keypad/tree/master/keypad raspi gpio keypad!

there's loads of youtube vidjos, might be one uses a dragndrop lib "macro keyboard"

https://blog.roastpotatoes.co/guide/2015/11/04/how-to-handwire-a-planck/

https://www.google.com/search?biw=1021&bih=853&sxsrf=ALeKk028tZvPPCoemMwFYh9WROct2z0I8Q%3A1613076455222&ei=55clYIaRDYS68gKFh4SABQ&q=write+your+own+keyboard+firmware+c%2B%2B&oq=write+your+own+keyboard+firmware&gs_lcp=Cgdnd3Mtd2l6EAMYADIFCCEQoAE6BAgjECc6BQgAEJECOggIABCxAxCDAToLCC4QsQMQxwEQowI6BAgAEEM6BQgAELEDOgcIABCxAxBDOgIIADoHCAAQhwIQFDoCCC46BQgAEMkDOgYIABAWEB46BQgAEIYDOggIIRAWEB0QHjoHCCEQChCgAToECCEQClCqrgZYzpIHYOGfB2gAcAJ4AIABmQGIAaEXkgEEMjcuNpgBAKABAaoBB2d3cy13aXrAAQE&sclient=gws-wiz

https://github.com/barrysims/quick-brown-fox

https://geekhack.org/index.php?topic=88908.0

https://deskthority.net/viewtopic.php?t=7177