The last-straw motivating reason I switched to nextcloud was because dropbox decided they wouldn't let me sync my files to an ecryptfs file system. (I believe they recanted on this policy a few months later.) I didn't like being held hostage to their bad design decisions, so I left and found a solution that worked better for me. Dropbox has also had some serious security vulnerabilities [1], which left me feeling less than confident in their ability to manage my personal data.
Thanks for the heads up, I see this confirmed at https://help.dropbox.com/installs-integrations/desktop/syste... under the list of supported file systems on Linux (which is currently ext4, zfs and xfs on 64 bit systems, eCryptFS backed by ext4, and btrfs).
[1] https://nakedsecurity.sophos.com/2011/06/21/dropbox-lets-any...