I'm running Pages 14 on my MAcBook Pro 2019 Sonoma 14.4.1. The 'Endnote citation is greyed out. How can I use citation?.

The Pages EndNote Citation Insert menu item is only enabled after you have installed:

• Pages EndNote Plug0in v3.3
• EndNote application X9.3 or later (EndNote 21.2 currently)

In this order, launch EndNote, then Pages, and the Insert menu : EndNote Citation menu item will be active.

Also, see the Related Article link above on this page.

I don't know if the "Related Article:" at the top of the page shows when you ask a question, but it should be visible, now. Take a look there for instructions on using EndNote Add-In. If you have the EndNote add-in installed, the links in the article might help describe which version is required.