You will want to edit the Theme in the user.css file. You will want to remove the css that manages hiding the Buddy List (Aka Friend Activity).
I would recommend you look into Khanhas new Repo spicetify-cli which is being worked on, while this Repo is no longer being maintained. The default Theme in the Spicetify-cli doesn't hide the Friends Tab.
You will want to edit the Theme in the user.css file. You will want to remove the css that manages hiding the Buddy List (Aka Friend Activity).
I would recommend you look into Khanhas new Repo spicetify-cli which is being worked on, while this Repo is no longer being maintained. The default Theme in the Spicetify-cli doesn't hide the Friends Tab.