Turning file vault on AFTER already using iCloud desktop and documents sync

Everything in iCloud is already encrypted. Enabling File Vault will have no added benefit for your cloud content.

The encryption process for the hard drive just chews through the data and encrypts it. It does not care what the files are or if they are synced elsewhere.

When syncing with iCloud, there is no detection of "this is encrypted" and "this is not encrypted" It's all just bits and bytes and up it goes to an encrypted storage location.

iCloud security and privacy overview - Apple Support

That's the way I understand the process to work.

By the time the iCloud's encryption process "sees" or "gets" the data it has been decrypted by OSX. It then encrypts it again for transport. Once on iCloud, their filesystem would encrypt again.

All invisible to the user.

Thanks.

I read the encryption is FDE, full disk encryption. Apple is, understandably, coy with the full details.

I am not sure if adding encryption would trigger an iCloud upload cycle. The file's contents to external apps are not changed. The "encrypt" "decrypt" cycle is done by the file system, not the app reading the file. Otherwise all OSX apps would need to be able to "encrypt/decrypt" to be of any value to a user. As they say, "there's people for that" I'm sure that's why you read about performance issues for encryption when an app has to "wait" for the process to finish for all read/writes.

Maybe pare down your Photo Library and test with turning Filevault on with a smallish library. Or just PAUSE uploading if it starts.

They remain in iCloud so that they will be in place the next time you log in to your account. What would you prefer to happen to them?

Any changes to the documents should cause them to resync.

Sorry.

I don't do voodoo or black magic!