Dropbox is asking me to change location to Ext4

Dropbox doesn't support eCryptfs.

As per this official documentation

Note: ecryptfs is not supported, but Dropbox will continue to sync with supported file systems that are encrypted via full disk encryption (e.g. LUKS)

Also another important note

If you’re running a supported operating system, but you see a message that your computer is unsupported, you may be running Dropbox in an unsupported configuration.