Questions about EA Games The Sims 4 - Island Living Add-On

Unfortunately not, all Sims 4 add-ons require an internet connection (i.e. online mode). Source: https://answers.ea.com/t5/Technical-Issues-PC/Expansions-won-t-work-in-offline-mode/td-p/7041621

This is effectively just an expansion without the main game, which is required....