I use Dropbox to store and sync files with my computers and I have it installed on my Linux Mintbox. Today I decided to install Dropbox on my Pixelbook but I couldn't get it to work because I kept being asked to move the Dropbox folder to another file system. Apparently, Dropbox recently made a change with their Linux support that requires the Dropbox folder to be on an ext4 file system. page 
Next I tried rclone but I couldn't get passed the authorization step in its install instructions.
Finally, I searched for Dropbox on Chromebook and found an article to add an app from the Chrome OS Webstore called Files System For Dropbox that adds a folder to the Chrome OS Files app.
After entering my Dropbox credentials, I see a Dropbox folder added to Files and I can now browse and open files directly from this folder.
The main reason why I want to add Dropbox to my Pixelbook is to experiment with a Tiddlywiki file that I will edit using Quine on my iPad Pro. Quine syncs with Dropbox and iCloud and I selected Dropbox to sync with.
Unfortunately, it appears the File System For Dropbox won't work as I want. I need to edit the Tiddlywiki file, but edits that I make don't seem to get saved back up to Dropbox. Right now I seem to only be able to manually download the file, edit it, then manually upload it.