Converting your drive to APFS is required if you want to keep storing your Dropbox folder on that external drive under macOS's modern architecture. Apple has transitioned cloud providers to its native File Provider API, which enforces strict filesystem constraints.
This is likely driven, at least in part, by Apple dropping support for encrypted HFS+ drives in macOS 28.
About support for encrypted Mac OS Extended disks in macOS 28 or later - Apple Support
Here is how the transition will impact your setup, your files, and your Parallels configuration:
Is Conversion Mandatory?
- For Dropbox on the External Drive: Yes. To continue syncing your Dropbox folder on an external drive under macOS, the drive must be formatted as APFS and encrypted.
- If you choose not to convert: Dropbox will eventually block syncing or force your Dropbox folder back to your Mac's internal drive (under ~/Library/CloudStorage)
Impact on Other Files
- Data Safety: Converting a Mac OS Extended (HFS+) drive to APFS through Mac's Disk Utility is technically a non-destructive "in-place" conversion. However, because you are also required by Dropbox to encrypt the drive, and because the WD My Book Duo is a mechanical hard drive (HDD), backing up your data first is absolutely critical.
- Performance on HDDs: APFS was designed for SSDs. While it works on mechanical drives, encrypting a large HDD and converting it to APFS can be an incredibly slow process that puts heavy stress on the drive.
Impact on Parallels Desktop & Windows Access
Converting to APFS should not change how Windows interacts with your drive in Parallels Desktop. Windows doesn’t natively mount HFS+ drives, so you must currently be mounting it as a network share. That will be the same for an APFS-formatted drive.
