Notion cannot let one automation trigger another, but you can update a related page from a button or from an automation that edits related pages directly.
- Make sure Page A and Page B are connected with a relation property.
- For an update triggered by a button: add a Button property to the database for Page A. In the button settings, choose "Add action" > "Edit property in" and select the relation property. Pick the property to change on the related page and set its value.
- For an update triggered by a change: open the database menu (the lightning bolt), choose Automations > New automation, and set the trigger to "Property edited" (for example Status). Then choose "Add action" > "Edit property in" and select the relation. Notion will update the linked page.
- If you need more than one change, add several actions inside the same automation. That avoids a chain of automations.
- For a calculated value instead of an action, use a rollup on Page B. A rollup reads from Page A through the relation and updates by itself, with no automation needed.
- Test by changing one record and confirming the related record updates.
Notion does not allow an automation's result to start another automation, so combine all the steps in one.
If it helps, I made a free starter template with this setup: https://2rds.github.io/freelancer-ops/lite.html?ref=notionanswers