There are a few posts on this topic, and I don’t think a solution was ever agreed upon. It can’t be done in standard Bubble – as the application owner/editor you can see all the data (except passwords).
Closest solution was putting all your data on an external database service that offered encryption, and having Bubble call it via APIs. But still, if encryption was a setting in the external service, you’d still have the ability to see the data, so I think the external service would have to be one where the data is encrypted by default and you as the application owner have zero ability to see it, even if you wanted.
PS: one of the posts is here: Encrypt database