Post count: 19

I think it is this line (but my linux knowledge is quite thin):

gamecon-gpio-rpi-dkms depends on dkms (>= 1.95); however:
Package dkms is not installed.

I don’t know why, but dkms should be there by default. But maybe there was a mistake earlier already?
Maybe you installed the wrong header files?

My suggestion is to ask for help from the developer of the db9 driver himself here:

Post your log there and you should get help by someone who does more than guessing… ;)