Both tools are in the similar space of a writing surface where you can track and visualize data, though Notion starts as a wiki whereas Coda begins as a doc. Our clients have found docs to be more familiar with their teams, especially as they grow.
Makers often hit limits when building internal tools in Notion, so they move to Coda for a rich formula language and building blocks like buttons, charts, and Packs (integrations) that can really grow a doc into an app.
Copy your words and tables from Notion into Coda and find the logical points to make new docs.