It’s up to you if you invest time or money. The FFXIV store offers three premium items that will automatically complete the A Realm Reborn, Heavensward, and Stormblood main scenario quests. This means that you need to be up to date with the Shadowbringers story to unlock the content that arrives with Endwalker.
You cannot advance into an expansion if you haven’t completed the story-driven quests from the previous expansion. Progress in Final Fantasy XIV is locked behind main scenario quests.