Encryption will not protect your privacy in the specific case of Dropbox.
They look into your activity, not files.
And that's pretty much standard for any kind of commercial SaaS, just because of security concerns.
Also, they are quite transparent about the provider they are using for internal activities (Stripe, etc.). Companies in EU will typically not disclose such information. For example, Dropbox disclose the use of AWS (for hosting the infra & code, I guess), whereas Proton does not disclose any hosting company.