This makes your Dropbox folder appear as if it's on an unencrypted Ext4 filesystem, no matter what filesystem you use, and you don't have to mount anything.
A Dropbox folder on a hard drive or partition, formatted with one of the following file system types: ext4; zfs; eCryptFS (back by ext4); xfs ... The Dropbox desktop app · The Dropbox mobile app · IPv6 addressing
Dropbox has announced that starting on November 7th 2018, only the ext4 file system will be supported in Linux for synchronizing folders in the Dropbox desktop ...