Dropbox does not offer zero knowledge encryption, and is able to decrypt and turn your data over to law enforcement if they are asked to do so. As someone who has used Dropbox for many years I always did so with an understanding that they would do so, and stored only appropriate data there.
For an individual or organization that wants to store data in the cloud but also wants or needs for it to be as close to completely secure as possible, the encryption tool that I prefer to use is Cryptomator, because it encrypts your data before ever sending it to Dropbox. Your files can be accessed on your local machine, but all Dropbox ever sees is the files after they have been encrypted.
I use this method to securely sync encrypted password databases across several different machines and am confident that even if my Dropbox account is compromised, my password databases will be secure. I wrote instructions for how to set up Cryptomator and published them here: https://www.alaskacomputerguy.com/category/howto/how-to-encrypt-dropbox-folder