Per the docs at
https://support.atlassian.com/cloud-automation/docs/create-automation-rules-in-confluence/
it says 4 things must not be true to see the 'automation' button at the top of pages in Confluence:
1) You're on the Space Overview page, a whiteboard, or a database. The automation icon appears only on pages in view mode.
(I am looking a regular page I just created)
2) You’re not an admin of the space you’re in (for Space automation).
(I have created a custom Automation rule via Space Settings > Automation, and it has Space scope, and I am a space admin)
3) You’re not a site admin or Confluence admin (for Global automation).
(N/A since the rule has space scope)
4) Your team has Cloud Standard or Cloud Free – automation is a premium feature in Confluence.
(How do I tell what we have? We are extensive Jira users and have 10s of thousands of Confluence pages, but I couldn't tell you which version we have...)