Hi @Edan_Ben-Atar,
There are ways to make the data secure, but you need to store it in different documents, requires more work to set up and have some drawbacks. But at least you definetly have many more options than in Notion.
Here you have some really good discussion about the topic: Unintuitive But Possibly More Secure Coda Publishing Setup – Looking for Feedback - Ask the Community - Coda Maker Community
I agree that there are some small features that would help a lot, specially regarding the discoverability of hidden data, but at least Coda has promised to work on it this year.