How can I fix backup errors on my SanDisk G Drive?

Sounds like you're running into a Time Machine (or other backup) process choking on an inaccessible or locked file in your user Library, particularly one used by Apple’s FileProvider system. This system is now deeply integrated into macOS, especially with iCloud Drive and third-party file providers, so dealing with its files can be a bit tricky.

First, I suggest that you don't use 'sudo launchctl unload.' This command is outdated. In modern macOS (especially anything post-Catalina), SIP (System Integrity Protection) blocks manipulation of system daemons like `fileproviderd` — which is why you're getting the "no such file" message.

Next, let's try to identify the faulty file provider, which in this case could be: Dropbox, Google Drive, or even a third-party app using Apple's File Provider API.

1. Open System Settings > Apple Account > iCloud > iCloud Drive > Options...
2. Uncheck any third-party app that you suspect might be syncing files via iCloud (e.g., PDF Expert, Notability, etc.)
3. We now want to switch to using the following command in the Terminal app: ls ~/Library/Application\ Support/FileProvider/ (Each folder you see there (like C4BD8175-C821-4ECE-BD7B-D9ED3D99EF3A) typically represents a container used by a File Provider extension — like iCloud Drive, OneDrive, Dropbox, or even app-specific cloud storage systems (like Readdle's PDF Expert, DEVONthink, etc)).
4. To find out which app a particular container belongs to, use this command: mdls ~/Library/Application\ Support/FileProvider/C4BD8175-C821-4ECE-BD7B-D9ED3D99EF3A (Look for kMDItemCFBundleIdentifier or related metadata. That might tell you what app created the folder.)

Once you figure out which app or service that folder is tied to:

• Disable the app’s sync (either via the app itself or System Settings > Internet Accounts).
• Then try your backup again.
• If it succeeds, you’ve identified the conflict — you can either live without that sync provider, or investigate updating or reinstalling it.

Unplug the drive. Then reconnect and try again.