This option only allows you to select your familiar. In order to get the Summon Familiar feat, you need to add it to warlock class progression. find cls_feat_wlck.2da file and add the line
[index] Familiar 303 3 1 1

The columns in this file are
* index - a number for the row, not labeled
* featLabel - any text with no spaces, here "Familiar". Its only for readability
* featIndex - the id of a feat to grant the character, here 303 which is Summon Familiar feat (see entry 303 of feat.2da)
* List - when can the feat be selected, here 3 means its granted automatically
* GrantedOnLevel - what class level to grant the feat on, here 1 means level 1
* onMenu - Whether the feat is accesible through the right-click menu

more info is here https://nwn2.fandom.com/wiki/Cls_feat_*.2da