The HN link is pg 2 of the forum thread; on page 1 a Dropbox employee states the following:
>The supported file systems are NTFS for Windows, HFS+ or APFS for Mac, and Ext4 for Linux.
>A supported file system is required as Dropbox relies on extended attributes (X-attrs) to identify files in the Dropbox folder and keep them in sync. We will keep supporting only the most common file systems that support X-attrs, so we can ensure stability and a consistent experience. (emphasis mine)[1]
XFS may support xattrs but that doesn't mean that Dropbox officially supports it. They are pretty clear on ext4 being the only supported filesystem.
>The supported file systems are NTFS for Windows, HFS+ or APFS for Mac, and Ext4 for Linux.
>A supported file system is required as Dropbox relies on extended attributes (X-attrs) to identify files in the Dropbox folder and keep them in sync. We will keep supporting only the most common file systems that support X-attrs, so we can ensure stability and a consistent experience. (emphasis mine)[1]
XFS may support xattrs but that doesn't mean that Dropbox officially supports it. They are pretty clear on ext4 being the only supported filesystem.
[1]https://www.dropboxforum.com/t5/Syncing-and-uploads/Linux-Dr...
Edit: added link to the proper comment in the Dropbox thread